Given a binary tree, find its maximum depth.The maximum depth is the number of nodes along the longest path from the root node down to the farthest leaf node.Show TagsShow Similar Proble

A city's skyline is the outer contour of the silhouette formed by all the buildings in that city when viewed from a distance. Now suppose you are given the locations and height of all the buildings as

Design and implement a data structure for Least Recently Used (LRU) cache. It should support the following operations: get and set.get(key) - Get the value (will always be positive) of the key if

Reverse a singly linked list.click to show more hints.Hint:A linked list can be reversed either iteratively or recursively. Could you implement both?使用迭代和递归实现单链表的反转。迭代的方法之间在剑指offer上面

Given a complete binary tree, count the number of nodes.Definition of a complete binary tree from Wikipedia:In a complete binary tree every level, except possibly the last, is completely fille

Given an integer array of size n, find all elements that appear more than ⌊ n/3 ⌋ times. The algorithm should run in linear time and in O(1) space.借助于Majority Element中的Boyer Moore算法，可以在O(1)的

Given 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.Follow up:What if the

Given an integer, write a function to determine if it is a power of two.Credits:Special thanks to @jianchao.li.fighter for adding this problem and creating all test cases.这道题有好多种解法。

Given 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 ancestor is defined between two node

Given a singly linked list, determine if it is a palindrome.Follow up:Could you do it in O(n) time and O(1) space?给定一个单链表，判断它的元素是否是回文。要求在O(n)的时间复杂度和O(1)的空间复杂度内求解。如果没有时间复杂度的限制，可以直接将链表反转再比较就

Given 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 is defined betw

Remove all elements from a linked list of integers that have value val.ExampleGiven: 1 --> 2 --> 6 --> 3 --> 4 --> 5 --> 6, val = 6Return: 1 --> 2 --> 3 --> 4 --> 5Credits:Special thanks

Write a function to delete a node (except the tail) in a singly linked list, given only access to that node.Supposed the linked list is 1 -> 2 -> 3 -> 4 and you are given the third node with val

Implement a basic calculator to evaluate a simple expression string.The expression string contains only non-negative integers, +, -, *, / operators and empty spaces . The integer division should trunca

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 n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it is able to trap after raining.For example, Given [0,1,0,2,1,0,1,3,2,1,2,1]

Given an array of n integers where n > 1, nums, return an array output such that output[i] is equal to the product of all the elements ofnums except nums[i].Solve it without division and in O(

Implement a basic calculator to evaluate a simple expression string.The expression string may contain open ( and closing parentheses ), the plus + or minus sign -, non-negative integers and empty space

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST.Calling next() will return the next smallest number in the BST.Note: next() and hasN

Given a binary tree, return the postorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3}, return [3,2,1].Note: Recursive solution is trivial, could you do it iteratively?二叉

Given a binary tree, return the preorder traversal of its nodes’ values.For example: Given binary tree {1,#,2,3}, return [1,2,3].Note: Recursive solution is trivial, could you do it iteratively?先序遍

Given 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, could you do it iteratively?二叉树的

Given an array of strings, return all groups of strings that are anagrams. Note: All inputs will be in lower-case.这道题是题目都没读懂，不知道Anagrams什么意思。Anagrams的意思是那些字符串的组成字符相同。比如说abc，那么abc这三个字符的所有排列都是Anagr

Given a string, find the length of the longest substring without repeating characters. For example, the longest substring without repeating letters for “abcabcbb” is “abc”, which the length is 3. For “

Given a string containing just the characters ‘(‘, ‘)’, ‘{‘, ‘}’, ‘[’ and ‘]’, determine if the input string is valid. The brackets must close in the correct order, “()” and “()[]{}” are all valid

Design a stack that supports push, pop, top, and retrieving the minimum element in constant time.push(x) – Push element x onto stack.pop() – Removes the element on top of the stack.top() – Get the t

Implement the following operations of a queue using stacks.push(x) – Push element x to the back of queue.pop() – Removes the element from in front of queue.peek() – Get the front element.empty() –

Implement the following operations of a stack using queues.push(x) – Push element x onto stack. pop() – Removes the element on top of the stack. top() – Get the top element. empty() – Return whether

Find the kth largest element in an unsorted array. Note that it is the kth largest element in the sorted order, not the kth distinct element.For example, Given [3,2,1,5,6,4] and k = 2, return 5.Note:

Given 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 element always

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”]. (O

Given a collection of integers that might contain duplicates, nums, return all possible subsets.Note: Elements in a subset must be in non-descending order. The solution set must not contain duplicate

The set [1,2,3,…,n] contains a total of n! unique permutations.By listing and labeling all of the permutations in order, We get the following sequence (ie, for n = 3):1 “123” 2 “132” 3 “213”

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 [

Follow up for N-Queens problem. Now, instead outputting board configurations, return the total number of distinct solutions. 和N-Queens 同样的解法。class Solution {public: int totalNQueens(int n

Given a digit string, return all possible letter combinations that the number could represent.A mapping of digit to letters (just like on the telephone buttons) is given below. Input:Digit string “2

The gray code is a binary numeral system where two successive values differ in only one bit.Given a non-negative integer n representing the total number of bits in the code, print the sequence of gray

Given n pairs of parentheses, write a function to generate all combinations of well-formed parentheses. For example, given n = 3, a solution set is: “((()))”, “(()())”, “(())()”, “()(())”, “(

Find all possible combinations of k numbers that add up to a number n, given that only numbers from 1 to 9 can be used and each combination should be a unique set of numbers. Ensure that numbers w

Given 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 the combinat