找到环的起点. 一快一慢相遇初,从头再走再相逢.…

动态规划属于技巧性比较强的题目,如果看到过原题的话,对解题很有帮助 55. Jump Game 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 maximum jump length at that position. Determine if you ar…

94. Binary Tree Inorder Traversal Given a binary tree, return the inorder traversal of its nodes' values. For example:Given binary tree [1,null,2,3], 1 \ 2 / 3 return [1,3,2]. Note: Recursive solution is trivial, could you do it iteratively? 非递归前序遍历:…

一般用dfs来做 最简单的一种: 17. Letter Combinations of a Phone Number Given a digit string, return all possible letter combinations that the number could represent. A mapping of digit to letters (just like on the telephone buttons) is given below. Input:Digit s…

需要注意overflow,特别是Integer.MIN_VALUE这个数字. 需要掌握二分法. 不用除法的除法,分而治之的乘方 2. Add Two Numbers You are given two linked lists representing two non-negative numbers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the tw…

137. Single Number II Given an array of integers, every element appears three times except for one. Find that single one. Note:Your algorithm should have a linear runtime complexity. Could you implement it without using extra memory? 记录32个bit每个bit出现的…

图论的常见题目有两类,一类是求两点间最短距离,另一类是拓扑排序,两种写起来都很烦. 求最短路径: 127. Word Ladder Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that: Only one letter can be…

1. 普通的二分法查找查找等于target的数字 2. 还可以查找小于target的数字中最小的数字和大于target的数字中最大的数字 由于新的查找结果总是比旧的查找结果更接近于target,因此只需不停更新result 3. 查找最接近于target的数字 这种情况下,新的查找结果不一定比旧的查找结果更接近target,所以要比较他们与target的差值. 题目: 74. Search a 2D Matrix Write an efficient algorithm that searche…

75. Sort Colors Given an array with n objects colored red, white or blue, sort them so that objects of the same color are adjacent, with the colors in the order red, white and blue. Here, we will use the integers 0, 1, and 2 to represent the color re…

71. Simplify Path Given an absolute path for a file (Unix-style), simplify it. For example,path = "/home/", => "/home"path = "/a/./b/../../c/", => "/c" Corner Cases: Did you consider the case where path = &quo…