Rotate Image You are given an n x n 2D matrix representing an image. Rotate the image by 90 degrees (clockwise). Follow up: Could you do this in-place? 在o(1)space中把题解掉。 思路是每次计算一个像素旋转后所到达的位置，发现四个像素构成了一个旋转的回路。于是只要存储这些像素的值，进行旋转即可。 需要注意循环的起止点。 class Solution { public: void rotate(vector<vector<int> > &matrix) { int n = matrix.size(); for(int i = 0; i < […]

Anagrams Given an array of strings, return all groups of strings that are anagrams. Note: All inputs will be in lower-case. anagrams变位词。 如：eat和tea，字母相同，只是排列顺序不同。 思路，用hashtable，先对string中的字母进行排序，这样所有的变位词都会变得相同。在hashtable中为一个入口，再利用unordered_map<string, MyStr>进行构建，需要注意，如果是第一次遇见相同的变位词的话，需要把当前str和在hashtable中的str都压入结果vector中。 class MyStr{ public: string str; bool isVisited; MyStr(string s, bool a):str(s),isVisited(a){} MyStr(){} }; class Solution { public: vector<string> anagrams(vector<string> &strs) { unordered_map<string, MyStr> h; vector<string> […]

Unique Binary Search Trees Given n, how many structurally unique BST’s (binary search trees) that store values 1…n? For example, Given n = 3, there are a total of 5 unique BST’s. 1 3 3 2 1 \ / / / \ \ 3 2 1 1 3 2 / […]

Subsets 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 contain duplicate subsets. For example, If S = [1,2,3], a solution is: [ [3], [1], [2], [1,2,3], [1,3], [2,3], [1,2], [] ] 深搜DFS。 […]

Word Search Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cell, where “adjacent” cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once. For example, […]

Partition List Given a linked list and a value x, partition it such that all nodes less than x come before nodes greater than or equal to x. You should preserve the original relative order of the nodes in each of the two partitions. For example, Given 1->4->3->2->5->2 and x […]

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 red, white, and blue […]

Path Sum II 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 and sum = 22, 5 / \ 4 8 / / \ 11 13 4 / \ / \ 7 2 […]

Jump Game II 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. Your goal is to reach the last index in the minimum number of jumps. For example: Given […]