Given an n-ary tree, return the preorder traversal of its nodes’ values.

In a array A of size 2N, there are N+1 unique elements, and exactly one of these elements is repeated N times.

输入: “abcabcbb”输出: 3 解释: 因为无重复字符的最长子串是 “abc”，所以其长度为 3。

For a binary tree T, we can define a flip operation as follows: choose any node, and swap the left and right child subtrees.

Given an array A of non-negative integers, half of the integers in A are odd, and half of the integers are even.

Write a class RecentCounter to count recent requests.

A string S of lowercase letters is given. We want to partition this string into as many parts as possible so that each letter appears in at most one part, and return a list of integers representing…

A full binary tree is a binary tree where each node has exactly 0 or 2 children.

We have a two dimensional matrix A where each value is 0 or 1.

Given an array of 2n integers, your task is to group these integers into n pairs of integer, say $(a_1, b_1), (a_2, b_2), \cdots, (a_n, b_n)$ which makes sum of $min(a_i, b_i)$ for all i from 1 to …