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

721. Accounts Merge <p> Given a list accounts, each element accounts[i] is a list of strings, where the first element accounts[i][0] is a name, and th

211. Add and Search Word - Data structure design <p> Design a data structure that supports the following two operations: <p> void addWord(word) bool s

67. Add Binary <p> Given two binary strings, return their sum (also ab binary string). <p> For example, ab = "11" b = "1" Return "100". <p> Company Ta

258. Add Digits <p> Given a non-negative integer num, repeatedly add all its digits until the result has only one digit. <p> For example: <p> Given nu

Given two double values as strings, return the sum of them as a string. You may not convert the string to a double. <p> E.g. "1.13" + "0.9" => "2.03"

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 contai

You are given two non-empty linked lists representing two non-negative integers. The most significant digit comes first and each of their nodes contai

Write a function addRecursive() that returns sum of two integers. The function should not use any of the arithmetic operators (+, ++, –, -, .. etc). <

306. Additive Number <p> Additive number is a string whose digits can form additive sequence. <p> A valid additive sequence should contain at least th

269. Alien Dictionary <p> There is a new alien language which uses the latin alphabet. However, the order among letters are unknown to you. You receiv

Given a tree, return whether the tree is almost balanced or not. The height different between the leaves of an almost balanced tree cannot exceed 1. N

Given an array of strings, return all groups of strings that are anagrams. <p> Note: All inputs will be in lower-case. <p> Tags: Hash table, String

Dijkstra Two-Stack Algorithm for Expression Evaluation Assumes that the expression is fully parenthesized, with numbers and characters separated by wh

413. Arithmetic Slices <p> A sequence of number is called arithmetic if it consists of at least three elements and if the difference between any two c

array generics resizing loitering iteration <p> void push(Item item) Item pop() boolean isEmpty() int size()

We are given an array asteroids of integers representing asteroids in a row. <p> For each asteroid, the absolute value represents its size, and the si

01 0 , can be 0 or 1 Generate all possible outputs Tags: Backtracking

Your AutocompleteSystem object will be instantiated and called as such: AutocompleteSystem obj = new AutocompleteSystem(sentences, times); List<String

637. Average of Levels in Binary Tree <p> Given a non-empty binary tree, return the average value of the nodes on each level in the form of an array.

Created by kiyan on 5/26/16.

Time: O(1), pop the top element on the stack Space: O(h), elements in the stack will never exceed the height of the tree

Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a BST. <p> Calling next() will return t

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

110. Balanced Binary Tree <p> Given a binary tree, determine if it is height-balanced. <p> For this problem, a height-balanced binary tree is defined

224. Basic Calculator <p> Implement a basic calculator to evaluate a simple expression string. <p> The expression string may contain open ( and closin

227. Basic Calculator II <p> Implement a basic calculator to evaluate a simple expression string. <p> The expression string contains only non-negative

121. Best Time to Buy and Sell Stock <p> Say you have an array for which the ith element is the price of a given stock on day i. <p> If you were only

Say you have an array for which the ith element is the price of a given stock on day i. <p> Design an algorithm to find the maximum profit. You may co

Say you have an array for which the ith element is the price of a given stock on day i. <p> If you were only permitted to complete at most one transac

Say you have an array for which the ith element is the price of a given stock on day i. <p> Design an algorithm to find the maximum profit. You may co

188. Best Time to Buy and Sell Stock IV <p> Say you have an array for which the ith element is the price of a given stock on day i. <p> Design an algo

714. Best Time to Buy and Sell Stock with Transaction Fee <p> Your are given an array of integers prices, for which the i-th element is the price of a

309. Best Time to Buy and Sell Stock with Cooldown <p> Say you have an array for which the ith element is the price of a given stock on day i. <p> Des

Best Time to Buy and Sell Stock Say 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

Binary Indexed Tree is represented as an array. Let the array be BITree[]. Each node of Binary Indexed Tree stores sum of some elements of given array

173. Binary Search Tree Iterator <p> Implement an iterator over a binary search tree (BST). Your iterator will be initialized with the root node of a

94. Binary Tree Inorder Traversal <p> Given a binary tree, return the inorder traversal of its nodes' values. <p> For example: Given binary tree [1,nu

102. Binary Tree Level Order Traversal <p> Given a binary tree, return the level order traversal of its nodes' values. (i.e., from left to right, leve

107. Binary Tree Level Order Traversal II <p> Given a binary tree, return the bottom-up level order traversal of its nodes' values. (ie, from left to

Given a binary tree, find the longest path from root to a leaf. The path can be arrow concatenated string like 1->2->3.

Given a binary tree, find the maximum path sum. <p> The path may start and end at any node in the tree. <p> For example: Given the below binary tree,

257. Binary Tree Paths <p> Given a binary tree, return all root-to-leaf paths. <p> For example, given the following binary tree: <p> | 1 | / \ |

145. Binary Tree Postorder Traversal <p> Given a binary tree, return the postorder traversal of its nodes' values. <p> Example: <p> Input: [1,null,2,3

Given a binary tree, return the preorder traversal of its nodes' values. <p> For example: Given binary tree {1,#,2,3}, 1 \ 2 / 3 return [1,2,3]. <p> N

Given a binary tree, imagine yourself standing on the right side of it, return the values of the nodes you can see ordered from top to bottom. <p> For

Given a binary tree, convert it to a Circular Doubly Linked List. <p> The left and right pointers in nodes are to be used as previous and next pointer

156. Binary Tree Upside Down <p> Given a binary tree where all the right nodes are either leaf nodes with a sibling (a left node that shares the same

314. Binary Tree Vertical Order Traversal <p> Given a binary tree, return the vertical order traversal of its nodes' values. (ie, from top to bottom,

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

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

401. Binary Watch <p> A binary watch has 4 LEDs on the top which represent the hours (0-11), and the 6 LEDs on the bottom represent the minutes (0-59)

201. Bitwise AND of Numbers Range <p> Given a range [m, n] where 0 <= m <= n <= 2147483647, return the bitwise AND of all numbers in this range, inclu

361. Bomb Enemy <p> Given a 2D grid, each cell is either a wall 'W', an enemy 'E' or empty '0' (the number zero), return the maximum enemies you can k

554. Brick Wall <p> There is a brick wall in front of you. The wall is rectangular and has several rows of bricks. The bricks have the same height but

Binary Search Tree node that contains an interval as value. Also has two children, left and right.

There are n bulbs that are initially off. You first turn on all the bulbs. Then, you turn off every second bulb. On the third round, you toggle every

299. Bulls and Cows <p> You are playing the following Bulls and Cows game with your friend: You write down a number and ask your friend to guess what

312. Burst Balloons <p> Given n balloons, indexed from 0 to n-1. Each balloon is painted with a number on it represented by array nums. You are asked

Given a string, return whether the characters in the string can form a palindrome. Follow up, generate all possible combinations.

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 r

Given: function: isFriend(a, b) Returns true iff b is treated as a friend by a group of persons, say, represented as an array

Given a String, output the characters in the String according to its frequency. <p> For example, given "banana", the output should be “a 3, n 2, b 1”

You 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 c

133. Clone Graph <p> Clone an undirected graph. Each node in the graph contains a label and a list of its neighbors. <p> OJ's undirected graph seriali

270. Closest Binary Search Tree Value <p> Given a non-empty binary search tree and a target value, find the value in the BST that is closest to the ta

272. Closest Binary Search Tree Value II <p> Given a non-empty binary search tree and a target value, find k values in the BST that are closest to the

742. Closest Leaf in a Binary Tree <p> Given a binary tree where every node has a unique value, and a target key k, find the value of the closest leaf

Unlike binary tree, binary search tree can be constructed with preorder + inorder traversal. So null node can be ignored, thus making the string more

You are given coins of different denominations and a total amount of money amount. Write a function to compute the fewest number of coins that you nee

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. <p> The same re

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. <p> Each

216. Combination Sum III <p> 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 an

377. Combination Sum IV <p> Given an integer array with all positive numbers and no duplicates, find the number of possible combinations that add up t

Given two integers n and k, return all possible combinations of k numbers out of 1 ... n. <p> For example, If n = 4 and k = 2, a solution is: | [ |

Compare two version numbers version1 and version1. If version1 > version2 return 1, if version1 < version2 return -1, otherwise return 0. <p> You may

Given inorder and postorder traversal of a tree, construct the binary tree. <p> Note: You may assume that duplicates do not exist in the tree. <p> Tag

105. Construct Binary Tree from Preorder and Inorder Traversal <p> Given preorder and inorder traversal of a tree, construct the binary tree <p> Note:

Construct Binary Tree from Inorder and Postorder Traversal Given inorder and postorder traversal of a tree, construct the binary tree. Tags: Tree Arra

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 endpo

Given an array of integers, find if the array contains any duplicates. Your function should return true if any value appears at least twice in the arr