给定一个数组 nums 和一个值 val，你需要原地移除所有数值等于 val 的元素，返回移除后数组的新长度。

这是一个经典的分治法解决的问题，关键在于我们如何将这个问题分解为更小的子问题。反过来想，这个子字符串一定不包含什么元素呢？当一个元素出现的总次数小于k，那么该元素一定不在子字符串中，只需要将其作为分…

Given an integer n, generate all structurally unique BST’s (binary search trees) that store values 1 … n.

Given n, how many structurally unique BST’s (binary search trees) that store values 1 … n?

Given a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtree of a node contains only nodes with keys less than the node’s key.The rig…

Given a binary tree, flatten it to a linked list in-place.

如果包含两个或两个以上字节，则起始字节以n个1和1个0开头，例如，如果该UTF8字符包含两个字节，则第一个字节以110开头，同理，三个字符的第一个字节以1110开头。剩余的字节必须以10开头。

For an undirected graph with tree characteristics, we can choose any node as the root. The result graph is then a rooted tree. Among all possible rooted trees, those with minimum height are called …

Given a binary treestruct Node { int val; Node *left; Node *right; Node *next;}Populate each next pointer to point to its next right node. If there is no next right node, the next pointer should be…

You are given a perfect binary tree where all leaves are on the same level, and every parent has two children. The binary tree has the following definition: