Leetcode - 随笔分类(第25页) - neverlandly

Leetcode: 4Sum

摘要：可以按照3Sum的思路来做，并以此类推，KSum的复杂度就是O(N^(k-1)). 在3Sum外面再套一层循环，相当于N次求3Sum 若还有时间，可以参考https://discuss.leetcode.com/topic/29585/7ms-java-code-win-over-100 有更多优化阅读全文

posted @ 2014-10-12 04:03 neverlandly 阅读(381) 评论(0) 推荐(0)

Leetcode: Reverse Words in a String

摘要：Given an input string, reverse the string word by word.For example,Given s = "the sky is blue",return "blue is sky the".click to show clarification.Cl... 阅读全文

posted @ 2014-10-11 23:56 neverlandly 阅读(352) 评论(0) 推荐(0)

Leetcode: Longest Consecutive Sequence

摘要：Best Solution: only scan one direction, If the number x is the start of a streak (i.e., x-1 is not in the set), then test y = x+1, x+2, x+3, ... and s 阅读全文

posted @ 2014-10-11 12:38 neverlandly 阅读(496) 评论(0) 推荐(0)

Leetcode: Spiral Matrix

摘要：难度：87，这道题跟 Rotate Image 很相似，都是需要把矩阵分割成层来处理，每一层都是按：1. 正上方；2. 正右方；3. 正下方；4. 正左方这种顺序添加元素到结果集合。实现中要注意两个细节，一个是因为题目中没有说明矩阵是不是方阵，因此要先判断一下行数和列数来确定螺旋的层数，mina(行阅读全文

posted @ 2014-10-11 07:51 neverlandly 阅读(447) 评论(0) 推荐(0)

Leetcode: Word Ladder

摘要：难度：96.这道题看似一个关于字符串操作的题目，其实要解决这个问题得用图的方法。我们先给题目进行图的映射，顶点则是每个字符串，然后两个字符串如果相差一个字符则我们进行连边。接下来看看这个方法的优势，注意到我们的字符集只有小写字母，而且字符串长度固定，假设是L。那么可以注意到每一个字符可以对应的边则有阅读全文

posted @ 2014-10-11 05:39 neverlandly 阅读(425) 评论(0) 推荐(0)

Leetcode: Simplify Path

摘要：Given an absolute path for a file (Unix-style), simplify it. For example, path = "/home/", => "/home" path = "/a/./b/../../c/", => "/c" 难度：85，虽然不难，但是里阅读全文

posted @ 2014-10-10 13:20 neverlandly 阅读(335) 评论(0) 推荐(0)

Leetcode: Max Points on a line

摘要：Given n points on a 2D plane, find the maximum number of points that lie on the same straight line.Brute Force的做法，N个点两两可以构成N(N-1)/2条线，我们可以找这N(N-1)/2条线... 阅读全文

posted @ 2014-10-10 08:32 neverlandly 阅读(408) 评论(0) 推荐(0)

Leetcode: Surrounded Regions

摘要：难度：92。这个题目用到的方法是图形学中的一个常用方法：Flood fill算法，其实就是从一个点出发对周围区域进行目标颜色的填充。背后的思想就是把一个矩阵看成一个图的结构，每个点看成结点，而边则是他上下左右的相邻点，然后进行一次广度或者深度优先搜索。这道题首先四个边缘上的‘O’点都不是被surr 阅读全文

posted @ 2014-10-10 04:01 neverlandly 阅读(555) 评论(0) 推荐(0)

Leetcode: 3Sum Closest

摘要：这道题跟3Sum很像，区别就是要维护一个最小的diff，求出和目标最近的三个和。brute force时间复杂度为O(n^3)，优化的解法是使用排序之后夹逼的方法，总的时间复杂度为O(n^2+nlogn)=(n^2),空间复杂度是O(n)。第二遍做法：第一遍做法：阅读全文

posted @ 2014-10-09 04:47 neverlandly 阅读(308) 评论(0) 推荐(0)

Leetcode: 3Sum

摘要：Best 做法：不用Extra Space, Time Complexity still O(N^2) Good syntax: // creating Arrays of String type String a[] = new String[] { "A", "B", "C", "D" }; / 阅读全文

posted @ 2014-10-08 13:16 neverlandly 阅读(454) 评论(0) 推荐(0)

Leetcode: Wildcard Matching

摘要：想法是建立一个2维的boolean数组，booleen[][] check = new boolean[s.length()+1][p.length()+1]，注意最好比string的length大一行和一列，来包括第0行和第0列的情况。这样初始化比较方便。check[m][n]表示s的前m个元素是阅读全文

posted @ 2014-10-08 10:36 neverlandly 阅读(643) 评论(0) 推荐(0)

Leetcode: Edit Distance

摘要：Given two words word1 and word2, find the minimum number of steps required to convert word1 to word2. (each operation is counted as 1 step.)You have t... 阅读全文

posted @ 2014-10-08 06:10 neverlandly 阅读(742) 评论(0) 推荐(0)

Leetcode: Best Time to Buy and Sell Stock III

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 @ 2014-10-06 13:35 neverlandly 阅读(1408) 评论(0) 推荐(0)

Leetcode: Combination Sum II

摘要：Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.Each numb... 阅读全文

posted @ 2014-10-06 12:10 neverlandly 阅读(398) 评论(0) 推荐(0)

Leetcode: Next Permutation

摘要：这道题的算法第一次可能有点难想，但是做过一次后就知道了 Shi Li Analysis（会好理解很多）: Starting from the last position, the first time we find that num[i]<num[i+1], we stop. The positi 阅读全文

posted @ 2014-10-06 08:08 neverlandly 阅读(628) 评论(0) 推荐(0)

Leetcode: Merge Intervals

摘要：这道题跟Insert Intervals这道题很像，最开头要先对Intervals里面的Interval排序一下，用到了java的Collections.sort(List<Interval> list, Comparator<? super Interval> c)。排序以Interval的st 阅读全文

posted @ 2014-10-06 06:36 neverlandly 阅读(593) 评论(0) 推荐(1)

Leetcode: Minimum Window Substring

摘要：难度：90 String问题里面有很多不好做的，动不动就DP什么的，参考了一些资料http://blog.csdn.net/fightforyourdream/article/details/17373203 For example,S = “ADOBECODEBANC”T = “ABC”Minim 阅读全文

posted @ 2014-10-06 01:45 neverlandly 阅读(593) 评论(0) 推荐(0)

Leetcode: Insert Interval

摘要：If output is List: If output is array: 24-27 line can also be 阅读全文

posted @ 2014-10-05 12:33 neverlandly 阅读(425) 评论(0) 推荐(0)

Leetcode: Scramble String

摘要：Given a string s1, we may represent it as a binary tree by partitioning it to two non-empty substrings recursively.Below is one possible representatio... 阅读全文

posted @ 2014-10-05 01:52 neverlandly 阅读(388) 评论(0) 推荐(1)

Leetcode: Maximal Rectangle

摘要：难度：90 这是一道非常综合的题目，要求在0-1矩阵中找出面积最大的全1矩阵。刚看到这道题会比较无从下手，brute force就是对于每个矩阵都看一下，总共有m(m+1)/2*n(n+1)/2个子矩阵（原理跟字符串子串类似，字符串的子串数有n(n+1)/2，只是这里是二维情形，所以是两个相乘），复阅读全文

posted @ 2014-09-22 05:56 neverlandly 阅读(434) 评论(0) 推荐(0)

随笔分类 - Leetcode