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

You are given an n x n 2D matrix representing an image. Rotate the image by 90 degrees (clockwise). Follow up: Could you do this in-place? class Solution { public: /* * clockwise rotate *

Given an unsorted integer array, find the first missing positive integer. For example, Given [1,2,0] return 3, and [3,4,-1,1] return 2. Your algorithm should run in O(n) time and uses constant

The count-and-say sequence is the sequence of integers beginning as follows: 1, 11, 21, 1211, 111221, ... 1 is read off as "one 1" or 11. 11 is read off as "two 1s" or 21. 21 is read off as 

Implement next permutation, which rearranges numbers into the lexicographically next greater permutation of numbers. If such arrangement is not possible, it must rearrange it as the lowest possible

Given an array and a value, remove all instances of that value in place and return the new length. Do not allocate extra space for another array, you must do this in place with constant memory.

Given a sorted array, remove the duplicates in place such that each element appear only once and return the new length. Do not allocate extra space for another array, you must do this in place with

Write a function to find the longest common prefix string amongst an array of strings.class Solution { public: string longestCommonPrefix(vector& strs) { string res; int h = strs.s

int -> Roman class Solution { public: string intToRoman(int num) { char* c[4][10]={ {"","I","II","III","IV","V","VI","VII","VIII","IX"}, {"","X","XX","XXX","XL","

Determine whether an integer is a palindrome. Do this without extra space. click to show spoilers. Some hints: Could negative integers be palindromes? (ie, -1) If you are thinking of convertin

以下几种情况要考虑到1，排除输入空格问题2，确定正负3，排除字母4，处理overflow class Solution { public: int myAtoi(string str) { if (str.empty()) return 0; int i = 0, sign = 1; while (i + 1 < str.size() && isspace(st

Reverse digits of an integer. Example1: x = 123, return 321 Example2: x = -123, return -321 click to show spoilers. Have you thought about this? Here are some good questions to ask before c

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 N A P L S I

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 matrix of m x n elements (m rows, n columns), return all elements of the matrix in spiral order. For example, Given the following matrix: [ [ 1, 2, 3 ], [ 4, 5, 6 ], [ 7, 8, 9 ] ]