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Binary Tree Zigzag Level Order TraversalGiven a binary tree, return the zigzag level order traversal of its nodes’ values. (ie, from left to right, then right to left for the next level and alternate b

Sum Root to Leaf NumbersGiven a binary tree containing digits from 0-9 only, each root-to-leaf path could represent a number.An example is the root-to-leaf path 1->2->3 which represents the number 123.

Binary Tree PathsGiven a binary tree, return all root-to-leaf paths.For example, given the following binary tree: 1 / \2 3 \ 5All root-to-leaf paths are:["1->2->5", "1->3"]解题思路代码如下：/**

Lowest Common Ancestor of a Binary Search TreeGiven a binary search tree (BST), find the lowest common ancestor (LCA) of two given nodes in the BST.According to the definition of LCA on Wikipedia: “The

Lowest Common Ancestor of a Binary TreeGiven a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.According to the definition of LCA on Wikipedia: “The lowest common ance

Flatten Binary Tree to Linked ListGiven a binary tree, flatten it to a linked list in-place.For example, Given 1 / \ 2 5 / \ \ 3 4 6The flattened tree should look like:1 \ 2

Populating Next Right Pointers in Each Node IIFollow up for problem “Populating Next Right Pointers in Each Node”.What if the given tree could be any binary tree? Would your previous solution still wor

House RobberYou are a professional robber planning to rob houses along a street. Each house has a certain amount of money stashed, the only constraint stopping you from robbing each of them is that adj

House Robber IINote: This is an extension of House Robber.After robbing those houses on that street, the thief has found himself a new place for his thievery so that he will not get too much attention.

Best Time to Buy and Sell StockSay you have an array for which the ith element is the price of a given stock on day i.If you were only permitted to complete at most one transaction (ie, buy one and sel

Binary Tree Postorder TraversalGiven a binary tree, return the postorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3},1 \ 2 /3return [3,2,1].Note: Recursive solution i

Binary Tree Preorder TraversalGiven a binary tree, return the preorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3},1 \ 2 /3return [1,2,3].Note: Recursive solution is

Binary Tree Inorder TraversalGiven a binary tree, return the inorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3}, return [1,3,2].Note: Recursive solution is trivial, cou

Combination Sum IIGiven a collection of candidate numbers (C) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.Each number in C may only be used once in

Symmetric TreeGiven a binary tree, check whether it is a mirror of itself (ie, symmetric around its center).For example, this binary tree is symmetric: But the following is not: Note: Bonus points

Construct Binary Tree from Inorder and Postorder TraversalGiven inorder and postorder traversal of a tree, construct the binary tree.Note: You may assume that duplicates do not exist in the tree.解题思路方

Binary Tree Maximum Path SumGiven a binary tree, find the maximum path sum.For this problem, a path is defined as any sequence of nodes from some starting node to any node in the tree along the parent-

Binary Tree Level Order Traversal IIGiven a binary tree, return the bottom-up level order traversal of its nodes’ values. (ie, from left to right, level by level from leaf to root).For example: Given

Convert Sorted Array to Binary Search TreeGiven an array where elements are sorted in ascending order, convert it to a height balanced BST.解题思路 为了得到高度平衡的二叉树，选中点 middle=(start+end)/2middle = (start + e

Balanced Binary TreeGiven a binary tree, determine if it is height-balanced.For this problem, a height-balanced binary tree is defined as a binary tree in which the depth of the two subtrees of every n

Minimum Depth of Binary TreeGiven a binary tree, find its minimum depth.The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.解题思路思路一：采用递归的思想

Best Time to Buy and Sell Stock IISay you have an array for which the ith element is the price of a given stock on day i.Design an algorithm to find the maximum profit. You may complete as many transac

Given a binary treestruct TreeLinkNode { TreeLinkNode *left; TreeLinkNode *right; TreeLinkNode *next;}Populate each next pointer to point to its next right node. If there is no next right node,

Kth Smallest Element in a BSTGiven a binary search tree, write a function kthSmallest to find the kth smallest element in it.Note: You may assume k is always valid, 1 ≤ k ≤ BST’s total elements.Follo

Climbing StairsYou are climbing a stair case. It takes n steps to reach to the top.Each time you can either climb 1 or 2 steps. In how many distinct ways can you climb to the top?解题思路class Solution {p

A robot is located at the top-left corner of a m x n grid (marked ‘Start’ in the diagram below).The robot can only move either down or right at any point in time. The robot is trying to reach the botto

Maximum SubarrayFind the contiguous subarray within an array (containing at least one number) which has the largest sum.For example, given the array [−2,1,−3,4,−1,2,1,−5,4], the contiguous subarray [4

Single Number IIGiven 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

Reverse BitsReverse bits of a given 32 bits unsigned integer.For example, given input 43261596 (represented in binary as 00000010100101000001111010011100), return 964176192 (represented in binary as 00

Number of 1 BitsWrite a function that takes an unsigned integer and returns the number of ’1’ bits it has (also known as the Hamming weight).For example, the 32-bit integer ’11’ has binary representati

Given a set of distinct integers, nums, 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 num

Single NumberGiven an array of integers, every element appears twice except for one. Find that single one.Note: Your algorithm should have a linear runtime complexity. Could you implement it without u

Majority ElementGiven an array of size n, find the majority element. The majority element is the element that appears more than ⌊ n/2 ⌋ times.You may assume that the array is non-empty and the majority

Decode WaysA message containing letters from A-Z is being encoded to numbers using the following mapping:'A' -> 1'B' -> 2...'Z' -> 26Given an encoded message containing digits, determine the total

Unique Paths IIFollow up for “Unique Paths”:Now consider if some obstacles are added to the grids. How many unique paths would there be?An obstacle and empty space is marked as 1 and 0 respectively in

Perfect SquaresGiven a positive integer n, find the least number of perfect square numbers (for example, 1, 4, 9, 16, ...) which sum to n.For example, given n = 12, return 3 because 12 = 4 + 4 + 4; giv

Ugly Number IIWrite a program to find the n-th ugly number.Ugly numbers are positive numbers whose prime factors only include 2, 3, 5. For example, 1, 2, 3, 4, 5, 6, 8, 9, 10, 12 is the sequence of the

Path SumGiven 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 and

Path Sum IIGiven 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,return 解题思路深度优先搜索。代码如下：/** * De

Maximal SquareGiven a 2D binary matrix filled with 0’s and 1’s, find the largest square containing all 1’s and return its area.For example, given the following matrix:1 0 1 0 01 0 1 1 11 1 1 1 11 0