2015 年 12月随笔档案 - neverlandly

Leetcode: Coin Change

摘要：You are given coins of different denominations and a total amount of money amount. Write a function to compute the fewest number of coins that you nee... 阅读全文

posted @ 2015-12-31 14:07 neverlandly 阅读(369) 评论(0) 推荐(0)

Leetcode: Best Time to Buy and Sell Stock with Cooldown

摘要：Say you have an array for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may complet... 阅读全文

posted @ 2015-12-31 13:15 neverlandly 阅读(874) 评论(0) 推荐(0)

Leetcode: Sparse Matrix Multiplication

摘要：Given two sparse matrices A and B, return the result of AB.You may assume that A's column number is equal to B's row number.Example:A = [ [ 1, 0, 0],... 阅读全文

posted @ 2015-12-31 07:57 neverlandly 阅读(2558) 评论(0) 推荐(0)

Leetcode: Expression Add Operators

摘要：参考http://segmentfault.com/a/1190000003797204 and http://blog.csdn.net/u013027996/article/details/48713751 深度优先搜索复杂度时间 O(N^2) 空间 O(N) 思路因为要输出所有可能的情况阅读全文

posted @ 2015-12-31 07:13 neverlandly 阅读(334) 评论(0) 推荐(0)

Leetcode: Remove Invalid Parentheses

摘要：Remove the minimum number of invalid parentheses in order to make the input string valid. Return all possible results. Note: The input string may cont 阅读全文

posted @ 2015-12-31 02:34 neverlandly 阅读(1487) 评论(0) 推荐(0)

Leetcode: Number of Connected Components in an Undirected Graph

摘要：Given n nodes labeled from 0 to n - 1 and a list of undirected edges (each edge is a pair of nodes), write a function to find the number of connected ... 阅读全文

posted @ 2015-12-30 13:04 neverlandly 阅读(2909) 评论(0) 推荐(0)

Leetcode: Number of Islands II && Summary of Union Find

摘要：Union Find Princeton's lecture note on Union Find in Algorithms and Data Structures It is a well organized note with clear illustration describing fro 阅读全文

posted @ 2015-12-30 08:09 neverlandly 阅读(3762) 评论(0) 推荐(0)

Leetcode: Additive Number

摘要：Additive number is a string whose digits can form additive sequence. A valid additive sequence should contain at least three numbers. Except for the f 阅读全文

posted @ 2015-12-30 05:13 neverlandly 阅读(330) 评论(0) 推荐(0)

Leetcode: Range Sum Query 2D - Immutable

摘要：阅读全文

posted @ 2015-12-29 09:25 neverlandly 阅读(323) 评论(0) 推荐(0)

Leetcode: Range Sum Query - Immutable

摘要：Given an integer array nums, find the sum of the elements between indices i and j (i ≤ j), inclusive. Example: Given nums = [-2, 0, 3, -5, 2, -1] sumR 阅读全文

posted @ 2015-12-29 08:56 neverlandly 阅读(238) 评论(0) 推荐(0)

Leetcode: Smallest Rectangle Enclosing Black Pixels

摘要：An image is represented by a binary matrix with 0 as a white pixel and 1 as a black pixel. The black pixels are connected, i.e., there is only one bla 阅读全文

posted @ 2015-12-29 08:28 neverlandly 阅读(946) 评论(0) 推荐(0)

Leetcode: Longest Increasing Subsequence

摘要：讲解一：用一个数组来存 the smallest tail of all increasing subsequences with length i+1 in tails[i]. For example, say we have nums = [4,5,6,3], then all the ava 阅读全文

posted @ 2015-12-29 06:07 neverlandly 阅读(430) 评论(0) 推荐(0)

Leetcode: Bulls and Cows

摘要：Be careful, when calculate B, you should exclude A's cases 阅读全文

posted @ 2015-12-29 04:52 neverlandly 阅读(340) 评论(0) 推荐(0)

Leetcode: Serialize and Deserialize Binary Tree

摘要：Referring this post: https://leetcode.com/problems/serialize-and-deserialize-binary-tree/discuss/74253/Easy-to-understand-Java-Solution But instead us 阅读全文

posted @ 2015-12-29 03:16 neverlandly 阅读(380) 评论(0) 推荐(0)

Leetcode: Binary Tree Longest Consecutive Sequence

摘要：递归法复杂度时间O(n) 空间O(h) 思路因为要找最长的连续路径，我们在遍历树的时候需要两个信息，一是目前连起来的路径（curLen）有多长（以当前节点为终点），二是目前路径的上一个节点的值(preVal)。每一次递归，先检查当前节点是否比上一节点大1, 是，curLen++, 否curL 阅读全文

posted @ 2015-12-29 01:11 neverlandly 阅读(366) 评论(0) 推荐(0)

Leetcode: Best Meeting Point

摘要：A group of two or more people wants to meet and minimize the total travel distance. You are given a 2D grid of values 0 or 1, where each 1 marks the h... 阅读全文

posted @ 2015-12-28 12:06 neverlandly 阅读(294) 评论(0) 推荐(0)

Leetcode: Find Median from Data Stream

摘要：最大最小堆复杂度时间 O(logN) insert, O(1) query, 空间 O(N) 思路维护一个最大堆，一个最小堆。最大堆存的是到目前为止较小的那一半数，最小堆存的是到目前为止较大的那一半数，这样中位数只有可能是堆顶或者堆顶两个数的均值。而维护两个堆的技巧在于判断堆顶数和新来的数的大阅读全文

posted @ 2015-12-28 07:45 neverlandly 阅读(286) 评论(0) 推荐(0)

Leetcode: Flip Game II

摘要：You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take tu 阅读全文

posted @ 2015-12-28 06:05 neverlandly 阅读(548) 评论(0) 推荐(0)

Leetcode: Flip Game

摘要：You are playing the following Flip Game with your friend: Given a string that contains only these two characters: + and -, you and your friend take tu... 阅读全文

posted @ 2015-12-28 04:17 neverlandly 阅读(307) 评论(0) 推荐(0)

Leetcode: Nim Game

摘要：You are playing the following Nim Game with your friend: There is a heap of stones on the table, each time one of you take turns to remove 1 to 3 ston... 阅读全文

posted @ 2015-12-28 02:17 neverlandly 阅读(233) 评论(0) 推荐(0)

Leetcode: Word Pattern II

摘要：Given a pattern and a string str, find if str follows the same pattern.Here follow means a full match, such that there is a bijection between a letter... 阅读全文

posted @ 2015-12-28 01:45 neverlandly 阅读(350) 评论(0) 推荐(0)

Leetcode: Word Pattern

摘要：Given a pattern and a string str, find if str follows the same pattern. Here follow means a full match, such that there is a bijection between a lette 阅读全文

posted @ 2015-12-28 00:54 neverlandly 阅读(335) 评论(0) 推荐(0)

Leetcode: Game of Life

摘要：编解码法复杂度时间 O(NN) 空间 O(1) 思路最简单的方法是再建一个矩阵保存，不过当inplace解时，如果我们直接根据每个点周围的存活数量来修改当前值，由于矩阵是顺序遍历的，这样会影响到下一个点的计算。如何在修改值的同时又保证下一个点的计算不会被影响呢？实际上我们只要将值稍作编码就行了阅读全文

posted @ 2015-12-27 13:18 neverlandly 阅读(513) 评论(0) 推荐(0)

Leetcode: Alien Dictionary && Summary: Topological Sort

摘要：There is a new alien language which uses the latin alphabet. However, the order among letters are unknown to you. You receive a list of words from the... 阅读全文

posted @ 2015-12-27 12:05 neverlandly 阅读(579) 评论(0) 推荐(0)

Leetcode: Unique Word Abbreviation

摘要：An abbreviation of a word follows the form . Below are some examples of word abbreviations:a) it --> it (no abbreviation) ... 阅读全文

posted @ 2015-12-27 07:14 neverlandly 阅读(389) 评论(0) 推荐(0)

Leetcode: Find the Duplicate Number

摘要：参考了这个总结，非常详细：http://segmentfault.com/a/1190000003817671 最好方法：映射找环法复杂度时间 O(N) 空间 O(1) 思路假设数组中没有重复，那我们可以做到这么一点，就是将数组的下标和1到n每一个数一对一的映射起来。比如数组是213,则映射阅读全文

posted @ 2015-12-26 13:56 neverlandly 阅读(328) 评论(0) 推荐(0)

Leetcode: Walls and Gates

摘要：Push all gates into queue first. Then for each gate update its neighbor cells who is empty and push them to the queue. Repeating above steps until the 阅读全文

posted @ 2015-12-26 13:14 neverlandly 阅读(405) 评论(0) 推荐(0)

Leetcode: Move Zeroes

摘要：第二遍做法：双指针压缩法：O(N), 空间：O(1) 实际上就是将所有的非0数向前尽可能的压缩，最后把没压缩的那部分全置0就行了。比如103040，先压缩成134，剩余的3为全置为0。过程中需要一个指针记录压缩到的位置。 Q：如果要把所有的0放在前面而不是后面呢？A：同样的解题思路，但是是从后向前阅读全文

posted @ 2015-12-26 09:51 neverlandly 阅读(362) 评论(0) 推荐(0)

Leetcode: Peeking Iterator

摘要：My thinking is: use a double cache: long cache, when no number is cached, cache = Long.MIN_VALUE. When i call next(), it will firstly check if there's 阅读全文

posted @ 2015-12-26 09:42 neverlandly 阅读(473) 评论(0) 推荐(0)

Leetcode: Inorder Successor in BST

摘要：网上看到更好的方法：https://leetcode.com/discuss/77805/java-5ms-short-code-with-explanations The idea is to compare root's value with p's value if root is not n 阅读全文

posted @ 2015-12-26 08:49 neverlandly 阅读(394) 评论(0) 推荐(0)

Leetcode: Zigzag Iterator

摘要：Best Solution: O(N) This solution also works for K vectors Use a queue to store the iterators in different vectors. Every time we call next(), we pop 阅读全文

posted @ 2015-12-26 08:11 neverlandly 阅读(357) 评论(0) 推荐(0)

Leetcode: Wiggle Sort

摘要：Given an unsorted array nums, reorder it in-place such that nums[0] = nums[2] = nums[i - 1]如果i是偶数，nums[i] nums[i - 1]，则交换以后肯定有nums[i] =nums[i-1])) {... 阅读全文

posted @ 2015-12-26 07:38 neverlandly 阅读(307) 评论(0) 推荐(0)

Leetcode: Perfect Squares

摘要：Given a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.For example, given n = 12, ... 阅读全文

posted @ 2015-12-26 04:57 neverlandly 阅读(265) 评论(0) 推荐(0)

Leetcode: First Bad Version

摘要：You are a product manager and currently leading a team to develop a new product. Unfortunately, the latest version of your product fails the quality c... 阅读全文

posted @ 2015-12-26 02:43 neverlandly 阅读(246) 评论(0) 推荐(0)

Leetcode: Find the Celebrity

摘要：最佳做法：O（N）time， O(1)space The first pass is to pick out the candidate. If candidate knows i, then switch candidate. The second pass is to check whether 阅读全文

posted @ 2015-12-26 01:46 neverlandly 阅读(384) 评论(0) 推荐(0)

Leetcode: Integer to English Words

摘要：Career Cup 150 Pg 442 Think of Convert(19,323,984) = Process(19) + "million" + Process(323) + "thousand" + Process(984) + "" The Process is a process 阅读全文

posted @ 2015-12-26 00:08 neverlandly 阅读(382) 评论(0) 推荐(0)

Leetcode: Paint Fence

摘要：There is a fence with n posts, each post can be painted with one of the k colors.You have to paint all the posts such that no more than two adjacent f... 阅读全文

posted @ 2015-12-25 05:59 neverlandly 阅读(791) 评论(0) 推荐(0)

Leetcode: H-Index II

摘要：Follow up for H-Index: What if the citations array is sorted in ascending order? Could you optimize your algorithm? Hint: Expected runtime complexity 阅读全文

posted @ 2015-12-25 03:10 neverlandly 阅读(435) 评论(0) 推荐(0)

Leetcode: H-Index

摘要：Hint: Sort first then scan: O(NlogN) time, O(1)space use another array: O(N) time, O(N) space（有点像counting sort）我们额外使用一个大小为N+1的数组stats。stats[i]表示有多少文章阅读全文

posted @ 2015-12-25 01:16 neverlandly 阅读(350) 评论(0) 推荐(0)

Leetcode: Closest Binary Search Tree Value II

摘要：Given a non-empty binary search tree and a target value, find k values in the BST that are closest to the target.Note:Given target value is a floating... 阅读全文

posted @ 2015-12-24 13:14 neverlandly 阅读(329) 评论(0) 推荐(0)

Leetcode: Encode and Decode Strings

摘要：If I choose / as spliter, how to ensure the other / wouldn't be seen as spliter? The idea is to store length of the str This one will be encoded as "6 阅读全文

posted @ 2015-12-24 12:27 neverlandly 阅读(458) 评论(0) 推荐(0)

Leetcode: Closest Binary Search Tree Value

摘要：Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the target.Note:Given target value is a floating... 阅读全文

posted @ 2015-12-24 09:47 neverlandly 阅读(301) 评论(0) 推荐(0)

Leetcode: Missing Number

摘要：Best Solution: Bit manipulation The basic idea is to use XOR operation. We all know that a^b^b =a, which means two xor operations with the same number 阅读全文

posted @ 2015-12-24 08:50 neverlandly 阅读(281) 评论(0) 推荐(0)

Leetcode: Graph Valid Tree && Summary: Detect cycle in undirected graph

摘要：This problem can be solved by using union find, reference this blog:https://segmentfault.com/a/1190000003791051 复杂度时间 O(N^M) 空间 O(N) 思路判断输入的边是否能构成一个阅读全文

posted @ 2015-12-24 02:58 neverlandly 阅读(1017) 评论(0) 推荐(0)

Leetcode: Paint House II

摘要：There are a row of n houses, each house can be painted with one of the k colors. The cost of painting each house with a certain color is different. Yo 阅读全文

posted @ 2015-12-23 13:31 neverlandly 阅读(995) 评论(0) 推荐(0)

Leetcode: Palindrome Permutation II

摘要：Given a string s, return all the palindromic permutations (without duplicates) of it. Return an empty list if no palindromic permutation could be form... 阅读全文

posted @ 2015-12-23 12:53 neverlandly 阅读(351) 评论(0) 推荐(0)

Leetcode: Palindrome Permutation

摘要：Given a string, determine if a permutation of the string could form a palindrome.For example,"code" -> False, "aab" -> True, "carerac" -> True.Hint:Co... 阅读全文

posted @ 2015-12-23 11:32 neverlandly 阅读(244) 评论(0) 推荐(0)

Leetcode: Ugly Number

摘要：Write a program to check whether a given number is an ugly number. Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For exa 阅读全文

posted @ 2015-12-23 06:59 neverlandly 阅读(235) 评论(0) 推荐(0)

Leetcode: Ugly Number II

摘要：Write a program to find the n-th ugly number.Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6... 阅读全文

posted @ 2015-12-23 06:48 neverlandly 阅读(278) 评论(0) 推荐(0)

Leetcode: Single Number III

摘要：Lintcode 也有这道题 Single Number III example: 1 0 1 0 0 0 1 0 1 0 0 0 0 0 1 0 0 0 0 0 1 0 0 0 1 0 0 1 0 0 1 0 0 1 0 0 0 0 1 0 0 0 0 0 1 0 0 1 如例所示，最后两个数8，阅读全文

posted @ 2015-12-23 05:43 neverlandly 阅读(233) 评论(0) 推荐(0)

Leetcode: 3Sum Smaller

摘要：Given an array of n integers nums and a target, find the number of index triplets i, j, k with 0 =2; i--) { 6 //if (i!=nums.length-1 && (n... 阅读全文

posted @ 2015-12-23 04:47 neverlandly 阅读(323) 评论(0) 推荐(0)

Leetcode: Factor Combinations

摘要：Numbers can be regarded as product of its factors. For example, 8 = 2 x 2 x 2; = 2 x 4. Write a function that takes an integer n and return all possib 阅读全文

posted @ 2015-12-23 02:33 neverlandly 阅读(478) 评论(0) 推荐(0)

Leetcode: Different Ways to Add Parentheses

摘要：用到了Divide and Conquer, 跟 Leetcode: Unique Binary Search Trees II 很像在input string里遍历各个operator, 依据每个operator分成左右子串，左右子串做递归返回所有可能的results，然后全排列。注意很巧妙的阅读全文

posted @ 2015-12-23 00:43 neverlandly 阅读(335) 评论(0) 推荐(0)

Leetcode: Add Digits

摘要：我的方法：注意最方便的获取一个数每一位的方法，是把它转化为String先，通过String.valueOf(int c) O（1）： http://my.oschina.net/Tsybius2014/blog/497645 另一个方法比较简单，可以举例说明一下。假设输入的数字是一个5位数字num，阅读全文

posted @ 2015-12-22 13:28 neverlandly 阅读(241) 评论(0) 推荐(0)

Leetcode: Binary Tree Paths

摘要：Given a binary tree, return all root-to-leaf paths.For example, given the following binary tree: 1 / \2 3 \ 5All root-to-leaf paths are:["1->... 阅读全文

posted @ 2015-12-22 12:44 neverlandly 阅读(278) 评论(0) 推荐(0)

Leetcode: Verify Preorder Sequence in Binary Search Tree

摘要：4 / \ 2 6 / \ / \ 1 3 5 7 如图所示BST， preorder结果是 4 2 1 3 6 5 7 4是root, 213是左子树，657是右子树 idea就是右子树不能再出现比root小的数，一旦出现，return false. 这样一层一层recursion, 直到子树只剩阅读全文

posted @ 2015-12-22 11:16 neverlandly 阅读(298) 评论(0) 推荐(0)

Leetcode: Meeting Rooms II

摘要：Like the previous one Meeting Room, still need to sort the intervals using a comparator. We need to simulate the process to know the maximum number of 阅读全文

posted @ 2015-12-22 09:19 neverlandly 阅读(951) 评论(0) 推荐(0)

Leetcode: Meeting Rooms

摘要：Interval as an array: Previous interval as an object: Implement a Comparator<Interval> Syntax: don't forget the public sign when defining a function 阅读全文

posted @ 2015-12-22 08:32 neverlandly 阅读(304) 评论(0) 推荐(0)

Leetcode: Flatten 2D Vector

摘要：Implement an iterator to flatten a 2d vector.For example,Given 2d vector =[ [1,2], [3], [4,5,6]]By calling next repeatedly until hasNext returns fa... 阅读全文

posted @ 2015-12-22 08:13 neverlandly 阅读(284) 评论(0) 推荐(0)

Leetcode: Count Univalue Subtrees

摘要：Given a binary tree, count the number of uni-value subtrees.A Uni-value subtree means all nodes of the subtree have the same value.For example:Given b... 阅读全文

posted @ 2015-12-22 07:22 neverlandly 阅读(1749) 评论(0) 推荐(0)

Leetcode: Group Shifted Strings

摘要：Given a string, we can "shift" each of its letter to its successive letter, for example: "abc" -> "bcd". We can keep "shifting" which forms the sequen... 阅读全文

posted @ 2015-12-22 02:04 neverlandly 阅读(444) 评论(0) 推荐(0)

Leetcode: Paint House

摘要：The same with F面经 Better Solution: O(N) time, O(1) space 阅读全文

posted @ 2015-12-21 13:34 neverlandly 阅读(339) 评论(0) 推荐(0)

Leetcode: Strobogrammatic Number III

摘要：A strobogrammatic number is a number that looks the same when rotated 180 degrees (looked at upside down).Write a function to count the total strobogr... 阅读全文

posted @ 2015-12-21 12:53 neverlandly 阅读(342) 评论(0) 推荐(0)

Leetcode: Strobogrammatic Number II

摘要：Watch out for cornor case: when n = 2, there shouldn't be "00" returned. but when n = 4, which uses n =2 as recursion base, "1001" is an answer 阅读全文

posted @ 2015-12-21 09:30 neverlandly 阅读(313) 评论(0) 推荐(0)

Leetcode: Strobogrammatic Number

摘要：Related to confusing number O(N) time and O(N) space O(N) time and O(1) space, use two pointers 阅读全文

posted @ 2015-12-21 07:11 neverlandly 阅读(293) 评论(0) 推荐(0)

Leetcode: Shortest Word Distance III

摘要：This is a follow up of Shortest Word Distance. The only difference is now word1 could be the same as word2.Given a list of words and two words word1 a... 阅读全文

posted @ 2015-12-21 06:40 neverlandly 阅读(284) 评论(0) 推荐(0)

Leetcode: Shortest Word Distance II

摘要：This is a follow up of Shortest Word Distance. The only difference is now you are given the list of words and your method will be called repeatedly ma... 阅读全文

posted @ 2015-12-21 04:34 neverlandly 阅读(323) 评论(0) 推荐(0)

Leetcode: Shortest Word Distance

摘要：双指针法：time O(N), space O(1) 一个指针指向word1上次出现的位置，一个指针指向word2上次出现的位置。因为两个单词如果比较接近的话，肯定是相邻的word1和word2的位置之差，所以我们只要每次得到一个新位置和另一个单词的位置比较一下就行了。阅读全文

posted @ 2015-12-21 00:57 neverlandly 阅读(309) 评论(0) 推荐(0)

Leetcode: Valid Anagram

摘要：还不知道Unicode 该怎么做只有lowercase alphabets的做法无外乎sort, hashmap, array, bitmap之类的 Better: Unicode Follow up In Java, a Unicode could be represented by a sin 阅读全文

posted @ 2015-12-20 13:24 neverlandly 阅读(333) 评论(0) 推荐(0)

Leetcode: Search a 2D Matrix II

摘要：Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties: Integers in each row are sorted i 阅读全文

posted @ 2015-12-20 12:42 neverlandly 阅读(251) 评论(0) 推荐(0)

Leetcode: Sliding Window Maximum

摘要：方法一：Heap时间 O(NlogK) 空间 O(K) maintain a maximum heap, notice PriorityQueue.remove(object o) can remove certain object from our heap. When writting Maxi 阅读全文

posted @ 2015-12-20 12:25 neverlandly 阅读(427) 评论(0) 推荐(0)

Leetcode: Product of Array Except Self

摘要：Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements of nums except ... 阅读全文

posted @ 2015-12-20 11:38 neverlandly 阅读(284) 评论(0) 推荐(0)

Leetcode: Delete Node in a Linked List

摘要：Write a function to delete a node (except the tail) in a singly linked list, given only access to that node. Supposed the linked list is 1 -> 2 -> 3 - 阅读全文

posted @ 2015-12-20 08:16 neverlandly 阅读(230) 评论(0) 推荐(0)

Leetcode: Lowest Common Ancestor of a Binary Tree

摘要：Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest... 阅读全文

posted @ 2015-12-20 08:08 neverlandly 阅读(271) 评论(0) 推荐(0)

Leetcode: Lowest Common Ancestor of a Binary Search Tree

摘要：Given a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST. According to the definition of LCA on Wikipedia 阅读全文

posted @ 2015-12-20 08:06 neverlandly 阅读(288) 评论(0) 推荐(0)

Leetcode: Palindrome Linked List

摘要：Given a singly linked list, determine if it is a palindrome.Follow up:Could you do it in O(n) time and O(1) space?先分成大小相同(可能长度差1) 两部分, reverse一个list. ... 阅读全文

posted @ 2015-12-20 07:12 neverlandly 阅读(290) 评论(0) 推荐(0)

Leetcode: Number of Digit One

摘要：Given an integer n, count the total number of digit 1 appearing in all non-negative integers less than or equal to n.For example:Given n = 13,Return 6... 阅读全文

posted @ 2015-12-20 05:21 neverlandly 阅读(262) 评论(0) 推荐(0)

Leetcode: Power of Two

摘要：Best Solution 还是有一个地方不小心：Integer.MIN_VALUE, 应该是false，但是因为只有一个1，我曾经判断为true。事实上，所有negative value都应该是false 一旦符号位为1，就return false，检查其他位只有1个1 做的时候遇到很多语法错误阅读全文

posted @ 2015-12-20 04:28 neverlandly 阅读(219) 评论(0) 推荐(0)

Leetcode: Implement Queue using Stacks

摘要：Implement the following operations of a queue using stacks.push(x) -- Push element x to the back of queue.pop() -- Removes the element from in front o... 阅读全文

posted @ 2015-12-20 02:20 neverlandly 阅读(276) 评论(0) 推荐(0)

Leetcode: Majority Element II

摘要：Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.Hin... 阅读全文

posted @ 2015-12-20 02:02 neverlandly 阅读(322) 评论(0) 推荐(0)

Leetcode: Summary Ranges

摘要：这种题就是要写的clean and tidy，好方法：维护两个指针的方法：阅读全文

posted @ 2015-12-19 13:33 neverlandly 阅读(271) 评论(0) 推荐(0)

Leetcode: Kth Smallest Element in a BST

摘要：Java Solution 1 - Inorder Traversal We can inorder traverse the tree and get the kth smallest element. Time is O(n). Recursion method: Java Solution 2 阅读全文

posted @ 2015-12-19 13:06 neverlandly 阅读(419) 评论(0) 推荐(0)

Leetcode: Basic Calculator II

摘要：用Stack来做：时间 O(N) 空间 O(N) 因为乘法和除法不仅要知道下一个数，也要知道上一个数。所以我们用一个栈把上次的数存起来，遇到加减法就直接将数字压入栈中，遇到乘除法就把栈顶拿出来乘或除一下新数，再压回去。最后我们把栈里所有数加起来就行了。上面这段code可以先用String.repl 阅读全文

posted @ 2015-12-19 12:31 neverlandly 阅读(314) 评论(0) 推荐(0)

Leetcode: Basic Calculator

摘要：https://discuss.leetcode.com/topic/15816/iterative-java-solution-with-stack 第二遍做法：遇到digit直接走到末尾，并且直接利用sign进行计算，这样比较方便第一遍做法：阅读全文

posted @ 2015-12-19 06:12 neverlandly 阅读(372) 评论(0) 推荐(0)

Leetcode: Count Complete Tree Nodes

摘要：递归树高法复杂度时间 O(N) 空间 O(1) 思路完全二叉树的一个性质是，如果左子树最左边的深度，等于右子树最右边的深度，说明这个二叉树是满的，即最后一层也是满的，则以该节点为根的树其节点一共有2^h-1个。如果不等于，则是左子树的节点数，加上右子树的节点数，加上自身这一个。注意这里在左阅读全文

posted @ 2015-12-19 02:30 neverlandly 阅读(336) 评论(0) 推荐(0)

Leetcode: Implement Stack using Queues

摘要：Implement the following operations of a stack using queues. push(x) -- Push element x onto stack. pop() -- Removes the element on top of the stack. to 阅读全文

posted @ 2015-12-19 01:31 neverlandly 阅读(273) 评论(0) 推荐(0)

Leetcode: Maximal Square

摘要：dp问题，用一个dp[i][j]保存matrix[i][j]作为右下节点的时候的最大矩形的边长 if (matrix[i][j] == '0') dp[i][j] = 0; else dp[i][j] = min(dp[i-1][j-1], dp[i-1][j], dp[i][j-1]) + 1; 阅读全文

posted @ 2015-12-19 00:47 neverlandly 阅读(351) 评论(0) 推荐(0)

Leetcode: Contains Duplicate III

摘要：暴力枚举会LTE，解题思路是用sortedSet来解决，sortedSet可以返回一个在某个范围的subSet，同时判断这个subSet是否为空即可解决，主要，本题需要使用long类型！时间 O(NlogK) 空间 O(K) 思路要求判断之前是否存在差值小于t的数字，我们需要知道在当前数字x两边阅读全文

posted @ 2015-12-18 23:31 neverlandly 阅读(274) 评论(0) 推荐(0)

Leetcode: Invert Binary Tree

摘要：nvert a binary tree. 4 / \ 2 7 / \ / \1 3 6 9to 4 / \ 7 2 / \ / \9 6 3 1Trivia:This problem was inspired by this... 阅读全文

posted @ 2015-12-18 13:14 neverlandly 阅读(291) 评论(0) 推荐(0)

Leetcode: The Skyline Problem

摘要：参考了http://www.cnblogs.com/tonyluis/p/4564617.html 复杂度 Time Complexity is O(n^2) because removal in a PQ is O(n), 空间 O(N) I think if replace PQ with Tr 阅读全文

posted @ 2015-12-18 12:27 neverlandly 阅读(271) 评论(0) 推荐(0)

Leetcode: Word Search II

摘要：如果跟Word Search做法一样，还按照DFS回溯的方法，逐个检查每个word是否在board里，显然效率是比较低的。我们可以利用Trie数据结构，也就是前缀树。然后dfs时，如果当前形成的单词不在Trie里，就没必要继续dfs下去了。如果当前字符串在trie里，就说明board可以形成这个wo 阅读全文

posted @ 2015-12-18 03:22 neverlandly 阅读(536) 评论(0) 推荐(0)

Leetcode: Rectangle Area

摘要：Find the total area covered by two rectilinear rectangles in a 2D plane.Each rectangle is defined by its bottom left corner and top right corner as sh... 阅读全文

posted @ 2015-12-18 00:48 neverlandly 阅读(325) 评论(0) 推荐(0)

Leetcode: Shortest Palindrome

摘要：本题最简单的思路是从后往前判断子串是否是回文串，然后把后面的弄到前面即可，不过这样仅仅能擦边通过测试 Brute Force: O(N^2), space O(1) DP: O(N^2), space O(N^2) KMP介绍：http://kb.cnblogs.com/page/176818/ 实阅读全文

posted @ 2015-12-17 14:43 neverlandly 阅读(303) 评论(0) 推荐(0)

Leetcode: Combination Sum III

摘要：ind all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a... 阅读全文

posted @ 2015-12-17 12:56 neverlandly 阅读(263) 评论(0) 推荐(0)

Leetcode: House Robber II

摘要：Analysis: if the last one is not robbed, then you are free to choose whether to rob the first one. you can break the circle by assuming the first hous 阅读全文

posted @ 2015-12-17 12:20 neverlandly 阅读(339) 评论(0) 推荐(0)

Leetcode: Contains Duplicate II

摘要：Given an array of integers and an integer k, find out whether there are two distinct indices i and j in the array such that nums[i] = nums[j] and the ... 阅读全文

posted @ 2015-12-17 07:44 neverlandly 阅读(201) 评论(0) 推荐(0)

Leetcode: Kth Largest Element in an Array

摘要：Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.For examp... 阅读全文

posted @ 2015-12-17 07:30 neverlandly 阅读(349) 评论(0) 推荐(0)

Leetcode: Contains Duplicate

摘要：Use HashSet: 阅读全文

posted @ 2015-12-17 07:01 neverlandly 阅读(200) 评论(0) 推荐(0)

Leetcode: Minimum Size Subarray Sum

摘要：Haven't think about the O(nlogn) solution. O(n) solution is to maintain a window My solution: shrink as much as possible while maintaining the window 阅读全文

posted @ 2015-12-17 06:52 neverlandly 阅读(292) 评论(0) 推荐(0)

Leetcode: Add and Search Word - Data structure design

摘要：方法1：brute force: search function compares each word with the pattern, time complexity: O(nk), n is number of words in dictionary, k is averge length 方阅读全文

posted @ 2015-12-17 06:46 neverlandly 阅读(623) 评论(0) 推荐(0)

Leetcode: Implement Trie (Prefix Tree) && Summary: Trie

摘要：参考百度百科：Trie树 a trie, also called digital tree and sometimes radix tree or prefix tree (as they can be searched by prefixes) The time complexity to ins 阅读全文

posted @ 2015-12-16 13:45 neverlandly 阅读(531) 评论(0) 推荐(0)

Leetcode: Course Schedule II

摘要：There are a total of n courses you have to take, labeled from 0 to n - 1. Some courses may have prerequisites, for example to take course 0 you have t 阅读全文

posted @ 2015-12-16 12:25 neverlandly 阅读(328) 评论(0) 推荐(0)

Leetcode: Course Schedule

摘要：The hint provided by leetcode is: Hints: BFS: 典型的拓扑排序。原理也很简单，在一个有向图中，每次找到一个没有前驱节点的节点（也就是入度为0的节点），然后把它指向其他节点的边都去掉，重复这个过程（BFS），直到所有节点已被找到，或者没有符合条件的节点（如果阅读全文

posted @ 2015-12-16 11:18 neverlandly 阅读(315) 评论(0) 推荐(0)

Leetcode: Isomorphic Strings

摘要：Best: O(N) time, constant space 复杂度时间 O(N) 空间 O(N) 思路用一个哈希表记录字符串s中字母到字符串t中字母的映射关系，一个集合记录已经映射过的字母。或者用两个哈希表记录双向的映射关系。这里不能只用一个哈希表，因为要排除egg->ddd这种多对一的映射阅读全文

posted @ 2015-12-15 11:46 neverlandly 阅读(335) 评论(0) 推荐(0)

Leetcode: Reverse Linked List

摘要：基本迭代 Time: O(N), Space: O(1) 基本递归 Time: O(N), Space: O(N)递归栈大小阅读全文

posted @ 2015-12-15 11:15 neverlandly 阅读(269) 评论(0) 推荐(0)

Leetcode: Count Primes

摘要：Count the number of prime numbers less than a non-negative number, n.Algorithm: The sieve of Eratosthenes,Referring to Summary: Primes0 and 1 are not ... 阅读全文

posted @ 2015-12-15 03:09 neverlandly 阅读(279) 评论(0) 推荐(0)

Leetcode: Remove Linked List Elements

摘要：set Dummy node 这题有个重要的follow up，就是在一个环里怎么删除节点：参考：http://www.cnblogs.com/EdwardLiu/p/5975748.html 阅读全文

posted @ 2015-12-15 02:24 neverlandly 阅读(270) 评论(0) 推荐(0)

Leetcode: Bitwise AND of Numbers Range

摘要：Given a range [m, n] where 0 maxRange) continue; 9 int mi = (m>>i) & 1;10 int ni = (n>>i) & 1;11 if (mi == 1 && n... 阅读全文

posted @ 2015-12-15 02:14 neverlandly 阅读(219) 评论(0) 推荐(0)

Leetcode: Happy Number

摘要：Write an algorithm to determine if a number is "happy". A happy number is a number defined by the following process: Starting with any positive intege 阅读全文

posted @ 2015-12-15 00:53 neverlandly 阅读(317) 评论(0) 推荐(0)