摘要：Given an array of non-negative integers, you are initially positioned at the first index of the array.Each element in the array represents your maximu... 阅读全文

摘要：Given a binary tree and a sum, find all root-to-leaf paths where each path's sum equals the given sum.For example:Given the below binary tree andsum =... 阅读全文

摘要：The count-and-say sequence is the sequence of integers beginning as follows:1, 11, 21, 1211, 111221, ...1is read off as"one 1"or11.11is read off as"tw... 阅读全文

摘要：Given a sorted array of integers, find the starting and ending position of a given target value.Your algorithm's runtime complexity must be in the ord... 阅读全文

摘要：Follow up for "Unique Paths":Now consider if some obstacles are added to the grids. How many unique paths would there be?An obstacle and empty space i... 阅读全文

摘要：Given a set of distinct integers,S, return all possible subsets.Note:Elements in a subset must be in non-descending order.The solution set must not co... 阅读全文

摘要：这道题是个细节实现题，只要把valid sudoku满足的三个条件判断一下即可。valid sudoku需满足下列三个条件：1）每一行数字1~9有且只出现一次。2）每一列数字1~9有且只出现一次。3）对于每个3*3的sub-box（用i=3、6，j=3、6两条线划分，总共9个sub-box）数字1~... 阅读全文

摘要：Given an unsorted array of integers, find the length of the longest consecutive elements sequence.For example,Given[100, 4, 200, 1, 3, 2],The longest ... 阅读全文

摘要：Given a string containing just the characters'(',')','{','}','['and']', determine if the input string is valid.The brackets must close in the correct ... 阅读全文

摘要：Givennnon-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.分析... 阅读全文

摘要：Determine whether an integer is a palindrome. Do this without extra space.按照palindrome的定义，负数一定不是palindrome number。而且palindrome number肯定是沿着中轴（可能为一个数或者两... 阅读全文

摘要：Given a binary tree containing digits from0-9only, each root-to-leaf path could represent a number.An example is the root-to-leaf path1->2->3which rep... 阅读全文

摘要：这道题可以用双指针的方法解，将两个指针p,q的距离保持在n-1，然后移动q到List的最后一个元素，那么此时p指向的便是the Nth node from the end。要删除这个node，要分两种情况，一种是该node为head，另一种该node是中间node。对于第一种情况，可以简单的采用以下... 阅读全文

摘要：Question: Given two integersnandk, return all possible combinations ofknumbers out of 1 ...n.要产生全部的combinations，我们需要一种有序的方式产生combination以达到既产生全部又没有重复的... 阅读全文

摘要：要搜索的对象是一个rotated sorted array，所以从直觉上时间复杂度应该不会超过O(logn)。解决这个题目的另一个思路就是先把pivot找出来，在这里我把pivot定义为数组中最小的那个数。所以下面要解决的便是能不能在O(logn)的时间找到pivot。沿着这个思路，然后综合rota... 阅读全文

摘要：这道题实质是用螺旋线的形式遍历二维数组，而且这种遍历方式有很强的规律性，从最外层开始一直到最里层，而且每层都按顺时针的方向遍历。根据这种规律性，我们可以用两层循环，在遍历的同时对二维数组对应元素重新赋值，第一层循环是层数遍历，第二层循环是每一层元素遍历（值得注意的一点是顺时针遍历）。class So... 阅读全文

摘要：Follow up for N-Queens problem.Now, instead outputting board configurations, return the total number of distinct solutions.分析：跟N-Queens一样，DFS+Backtrac... 阅读全文

摘要：Then-queens puzzle is the problem of placingnqueens on ann×nchessboard such that no two queens attack each other.Given an integern, return all distinc... 阅读全文

摘要：最近做Leetcode上的题目，感觉有些挺有趣的，比如这个Single Number题目：Given an array of integers, every element appearstwiceexcept for one. Find that single one.Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory?如果没有时间和空间复杂度的限制，这道题并没有什么难处，大可以扫一遍数组，然后用hashmap记录每个数值出 阅读全文