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题目：https://oj.leetcode.com/problems/validate-binary-search-tree/Given a binary tree, determine if it is a valid binary search tree (BST).Assume a BST is defined as follows:The left subtr

题目：https://oj.leetcode.com/problems/binary-tree-postorder-traversal/Given a binary tree, return the postorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3},

题目：https://oj.leetcode.com/problems/combination-sum-ii/Given a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums t

题目：https://oj.leetcode.com/problems/balanced-binary-tree/Given a binary tree, determine if it is height-balanced.For this problem, a height-balanced binary tree is defined as a binary tree i

题目：https://oj.leetcode.com/problems/swap-nodes-in-pairs/Given a linked list, swap every two adjacent nodes and return its head.For example,Given 1->2->3->4, you should return the list as 2

题目：https://oj.leetcode.com/problems/binary-tree-preorder-traversal/Given a binary tree, return the preorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1

题目：https://oj.leetcode.com/problems/remove-duplicates-from-sorted-list-ii/Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the origina

题目：https://oj.leetcode.com/problems/binary-tree-level-order-traversal/Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).For

题目：https://oj.leetcode.com/problems/binary-tree-inorder-traversal/Given a binary tree, return the inorder traversal of its nodes' values.For example:Given binary tree {1,#,2,3}, 1

题目：https://oj.leetcode.com/problems/combination-sum/Given a set of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.Th

题目：https://oj.leetcode.com/problems/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

题目：https://oj.leetcode.com/problems/interleaving-string/Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2.For example,Given:s1 = "aabcc",s2 = "dbbca",Whe

题目：https://oj.leetcode.com/problems/word-break/Given a string s and a dictionary of words dict, determine if s can be segmented into a space-separated sequence of one or more dictionary words.

Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length.Do not allocate extra space for another array, you must do this in place with

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题目：Follow up for "Remove Duplicates":What if duplicates are allowed at most twice?For example,Given sorted array A = [1,1,1,2,2,3],Your function should return length = 5, and A is no

题目：Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.For example:Given the below binary tree

题目：https://oj.leetcode.com/problems/partition-list/

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题目：https://oj.leetcode.com/problems/unique-binary-search-trees/

题目：https://oj.leetcode.com/problems/string-to-integer-atoi/Implement atoi to convert a string to an integer.Hint: Carefully consider all possible input cases. If you want a challenge, please d

题目：https://oj.leetcode.com/problems/word-break-ii/Given a string s and a dictionary of words dict, add spaces in s to construct a sentence where each word is a valid dictionary word.Return a

题目：https://oj.leetcode.com/problems/search-in-rotated-sorted-array/Suppose a sorted array is rotated at some pivot unknown to you beforehand.(i.e., 0 1 2 4 5 6 7 might become 4 5 6 7 0 1 2

题目：https://oj.leetcode.com/problems/powx-n/

题目：https://oj.leetcode.com/problems/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 r

题目：https://oj.leetcode.com/problems/first-missing-positive/Given an unsorted integer array, find the first missing positive integer.For example,Given [1,2,0] return 3,and [3,4,-1,1] retu

题目：Evaluate the value of an arithmetic expression in Reverse Polish Notation.Valid operators are +, -, *, /. Each operand may be an integer or another expression.Some examples: ["

题目：https://oj.leetcode.com/problems/two-sum/Given an array of integers, find two numbers such that they add up to a specific target number.The function twoSum should return indices of the tw

题目：https://oj.leetcode.com/problems/linked-list-cycle/

题目：https://oj.leetcode.com/problems/sort-list/ort a linked list in O(n log n) time using constant space complexity.分析：

题目：https://oj.leetcode.com/problems/permutations/Given a collection of numbers, return all possible permutations.For example,[1,2,3] have the following permutations:[1,2,3], [1,3,2], [2,

题目：https://oj.leetcode.com/problems/reverse-words-in-a-string/

题目：https://oj.leetcode.com/problems/single-number-ii/

题目：https://oj.leetcode.com/problems/single-number/Given an array of integers, every element appears twice except for one. Find that single one.Note:Your algorithm should have a linear runt

题目：https://oj.leetcode.com/problems/subsets-ii/

题目：https://oj.leetcode.com/problems/3sum/

题目：https://oj.leetcode.com/problems/sum-root-to-leaf-numbers/

题目：https://oj.leetcode.com/problems/sqrtx/Implement int sqrt(int x).Compute and return the square root of x.分析：erfenchazhao

题目：https://oj.leetcode.com/problems/decode-ways/A message containing letters from A-Z is being encoded to numbers using the following mapping:'A' -> 1'B' -> 2...'Z' -> 26Given an enc

题目：https://oj.leetcode.com/problems/minimum-path-sum/Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which minimizes the sum of all numbers along i