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 paths are there?
Given an unsorted integer array, find the smallest missing positive integer.
Example 1:
Input: [1,2,0] Output: 3Example 2:
Input: [3,4,-1,1] Output: 2Example 3:
Input: [7,8,9,11,12] Output: 1Note:
- Your algorithm should run in O(n) time and uses constant extra space.
使用O(n)的时间复杂度和O(1)的空间在无序数组中查找第一个缺失的正数。
Given two non-negative integers
num1andnum2represented as strings, return the product ofnum1andnum2, also represented as a string.Example 1:
Input: num1 = “2”, num2 = “3” Output: “6”
Example 2:
Input: num1 = “123”, num2 = “456” Output: “56088”
将两个字符串表示的数字相乘（大数相乘）。
Given a collection of candidate numbers (
candidates) and a target number (target), find all unique combinations in candidates where thecandidatenumbers sums totarget.Each number in
candidatesmay only be used once in the combination.Note:
All numbers (including
target) will be positive integers. The solution set must not contain duplicate combinations.
Given a set of candidate numbers (
candidates) (without duplicates) and a target number (target), find all unique combinations incandidateswhere the candidate numbers sums totarget.The same repeated number may be chosen from candidates unlimited number of times.
Note:
- All numbers (including
target) will be positive integers.- The solution set must not contain duplicate combinations.
Determine if a 9x9 Sudoku board is valid. Only the filled cells need to be validated according to the following rules:
- Each row must contain the digits
1-9without repetition.- Each column must contain the digits
1-9without repetition.- Each of the 9
3x3sub-boxes of the grid must contain the digits1-9without repetition.
A partially filled sudoku which is valid.
The Sudoku board could be partially filled, where empty cells are filled with the character
'.'.
验证数独
Search in Rotated Sorted Array
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]).You are given a target value to search. If found in the array return its index, otherwise return
-1.You may assume no duplicate exists in the array.
Your algorithm’s runtime complexity must be in the order of
O(log n).
Given a string containing just the characters
'('and')', find the length of the longest valid (well-formed) parentheses substring. Example 1:Input: "(()" Output: 2 Explanation: The longest valid parentheses substring is "()"
输出最长的左右括号匹配的子串长度
