LchinaM的专栏

1. preorder travelclass Solution {public: vector preorderTraversal(TreeNode* root) { vector result; stack myStack; TreeNode * temp = root; while(!myStack.empty()

Given inorder and postorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.recursive answer:class Solution {public: TreeNode

Given preorder and inorder traversal of a tree, construct the binary tree.Note:You may assume that duplicates do not exist in the tree.recursive answer:递归方法：在preorder找到root节点，接着在inorder里找到ro

Given 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 between).For example:Given binary

Given a binary tree, return the level order traversal of its nodes' values. (ie, from left to right, level by level).For example:Given binary tree [3,9,20,null,null,15,7], 3 / \ 9 2

Given two binary trees, write a function to check if they are equal or not.Two binary trees are considered equal if they are structurally identical and the nodes have the same value.answer:

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.Th

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.Example:Input: "babad"Output: "bab"Note: "aba" is also a valid answer.

Given a string, find the length of the longest substring without repeating characters.Examples:Given "abcabcbb", the answer is "abc", which the length is 3.Given "bbbbb", the answer is "

You are given two non-empty linked lists representing two non-negative integers. The digits are stored in reverse order and each of their nodes contain a single digit. Add the two numbers and return i

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 \

Given a binary tree, return the inorder traversal of its nodes' values.For example:Given binary tree [1,null,2,3], 1 \ 2 / 3return [1,3,2].recursive solution:

Given a string containing only digits, restore it by returning all possible valid IP address combinations.For example:Given "25525511135",return ["255.255.11.135", "255.255.111.35"]. (Order

Reverse a linked list from position m to n. Do it in-place and in one-pass.For example:Given 1->2->3->4->5->NULL, m = 2 and n = 4,return 1->4->3->2->5->NULL.Note:Given m, n satisfy the

A 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 nu

Given an array of integers, return indices of the two numbers such that they add up to a specific target.You may assume that each input would have exactly one solution, and you may not use the sam

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 string "PAYPALISHIRING" is written in a zigzag pattern on a given number of rows like this: (you may want to display this pattern in a fixed font for better legibility)P A H NA P L S I

Implement atoi to convert a string to an integer.Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input ca

Given an array where elements are sorted in ascending order, convert it to a height balanced BST.answer:class Solution {public: TreeNode* sortedArrayToBST(vector& nums) { return myATB

Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine if s can be segmented into a space-separated sequence of one or more dictionary words. You may as

Given an array of integers, every element appears three times except for one, which appears exactly once. Find that single one.Note:Your algorithm should have a linear runtime complexity. Coul

There are N children standing in a line. Each child is assigned a rating value.You are giving candies to these children subjected to the following requirements:Each child must have at least on

There are N gas stations along a circular route, where the amount of gas at station i is gas[i].You have a car with an unlimited gas tank and it costs cost[i] of gas to travel from station i to

Given a string s, partition s such that every substring of the partition is a palindrome.Return all possible palindrome partitioning of s.For example, given s = "aab",Return[ ["aa","b"], [

A peak element is an element that is greater than its neighbors.Given an input array where num[i] ≠ num[i+1], find a peak element and return its index.The array may contain multiple peaks, in

Follow up for "Find Minimum in Rotated Sorted Array":What if duplicates are allowed?Would this affect the run-time complexity? How and why?Suppose an array sorted in ascending order is rotated

Suppose an array sorted in ascending order 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).Find the minimum element.You may assume no

Find the contiguous subarray within an array (containing at least one number) which has the largest product.For example, given the array [2,3,-2,4],the contiguous subarray [2,3] has the larges

Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:Only one letter can be changed at a

Given a triangle, find the minimum path sum from top to bottom. Each step you may move to adjacent numbers on the row below.For example, given the following triangle[ [2], [3,4], [

Given an array S of n integers, are there elements a, b, c in S such that a + b + c = 0? Find all unique triplets in the array which gives the sum of zero.Note: The solution set must not contain

Given an integer, convert it to a roman numeral.Input is guaranteed to be within the range from 1 to 3999.answer:class Solution {public: string intToRoman(int num) { string th

Given n non-negative integers a1, a2, ..., an, where each represents a point at coordinate (i, ai). n vertical lines are drawn such that the two endpoints of line i is at (i, ai) and (i, 0). Fin

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 / \

Given a singly linked list where elements are sorted in ascending order, convert it to a height balanced BST.answer:class Solution {public: TreeNode* sortedListToBST(ListNode* head) {

Given a sorted linked list, delete all nodes that have duplicate numbers, leaving only distinct numbers from the original list.For example,Given 1->2->3->3->4->4->5, return 1->2->5.Given 1->

Suppose an array sorted in ascending order 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).Write a function to determine if a given target

Given a set of distinct integers, nums, return all possible subsets.Note: The solution set must not contain duplicate subsets.For example,If nums = [1,2,3], a solution is:[ [3], [1],

Given a set of candidate numbers (C) (without duplicates) and a target number (T), find all unique combinations in C where the candidate numbers sums to T.The same repeated number may be chosen