Description: Count the number of prime numbers less than a non-negative number, n.

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?

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?

Given two sorted integer arrays nums1 and nums2, merge nums2 into nums1 as one sorted array.Note: You may assume that nums1 has enough space (size that is greater or equal to m + n) to hold additional elements from nums2. The number of elements initialized in nums1 and nums2 are m and n respectiv...

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 climb to the top?

Given two binary strings, return their sum (also a binary string). For example, a = "11" b = "1" Return "100".

Given a string S and a string T, find the minimum window in S which will contain all the characters in T in complexity O(n). For example, S = "ADOBECODEBANC" T = "ABC" Minimum window is "BANC". Note: If there is no such window in S that covers all characters in T, return the emtpy string "". If t...

Implement strStr().Returns the index of the first occurrence of needle in haystack, or -1 if needle is not part of haystack.

Find the total area covered by two rectilinear rectangles in a 2D plane. Each rectangle is defined by its bottom left corner and top right corner as shown in the figure. Rectangle Area Assume that the total area is never beyond the maximum possible value of int.

Rotate an array of n elements to the right by k steps. For example, with n = 7 and k = 3, the array [1,2,3,4,5,6,7] is rotated to [5,6,7,1,2,3,4].

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: You may assume k is always valid, 1 ≤ k ≤ array's length.

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 BST is modified (insert/delete operations) often and you need to find the kth smallest frequently? How woul...

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 does not matter)

Given 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 using extra memory?

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. For example, given s = "leetcode", dict = ["leet", "code"]. Return true because "leetcode" can be segmented as "leet code".

Given two words (beginWord and endWord), and a dictionary, find the length of shortest transformation sequence from beginWord to endWord,such that: Only one letter can be changed at a time Each intermediate word must exist in the dictionary For example, Given: start = "hit" end = "cog" dict = ["h...

我们知道必定存在这么两个整数a和b,a^2 <= sqrt(x) <= b^2，所以我们要做的其实就是缩小这个ab的范围。使用二分法解这题时，通过比较mid^2和x大小来确定我们在哪一个半片中搜索。

Given a 2D board and a word, find if the word exists in the grid. The word can be constructed from letters of sequentially adjacent cell, where "adjacent" cells are those horizontally or vertically neighboring. The same letter cell may not be used more than once. For example, Given board = {代码....

A linked list is given such that each node contains an additional random pointer which could point to any node in the list or null. Return a deep copy of the list.

Given a binary tree, find the maximum path sum. The path may start and end at any node in the tree. For example: Given the below binary tree, {代码...} Return 6.

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 and sum = 22, {代码...} return true, as there exist a root-to-leaf path 5->4->11->2 which sum is 22.

Given a binary tree, return the preorder traversal of its nodes' values. For example: Given binary tree {1,#,2,3}, {代码...} return [1,2,3].

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. For example: Given the following binary tree, {代码...} You should return [1, 3, 4].

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 between two nodes v and w as the lowest node in T that has both v and w as descendants (where we allow a n...

Given 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 node never differ by more than 1.

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 {代码...} The minimum path sum from top to bottom is 11 (i.e., 2 + 3 + 5 + 1 = 11).

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 bottom-right corner of the grid (marked 'Finish' in the diagram below). How many possible unique pat...

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.

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 value 3, the linked list should become 1 -> 2 -> 4 after calling your function.

Given n non-negative integers representing the histogram's bar height where the width of each bar is 1, find the area of largest rectangle in the histogram. Above is a histogram where width of each bar is 1, given height = [2,1,5,6,2,3].The largest rectangle is shown in the shaded area, which has...