[LeetCode] 62. Unique Paths_ Medium tag: Dynamic Programming
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?
Above is a 7 x 3 grid. How many possible unique paths are there?
Note: m and n will be at most 100.
Example 1:
Input: m = 3, n = 2
Output: 3
Explanation:
From the top-left corner, there are a total of 3 ways to reach the bottom-right corner:
1. Right -> Right -> Down
2. Right -> Down -> Right
3. Down -> Right -> Right
Example 2:
Input: m = 7, n = 3
Output: 28
这个题目思路就是dynamic programming, A[i][j] = A[i-1][j] + A[i][j-1] , i, j >= 1. T: O(m*n) , S: O(n) optimal(用滚动数组)
1. Constraints.
1) size [0*0] - [100*100]
2) edge case, m==0 or n ==0 => 0
2. Ideas
DP T: O(m*n) S; O(m*n)
3. Codes
1) T: O(m*n) , S: O(m*n)
class Solution:
def uniquePaths(self, m, n):
if m == 0 or n == 0: return
ans = [[1]*n for _ in range(m)]
for i in range(1, m):
for j in range(1, n):
ans[i][j] = ans[i-1][j] + ans[i][j-1]
return ans[-1][-1]
# or return ans[m-1][n-1]
2) T: O(m*n) , S: O(n) 滚动数组
class Solution:
def uniquePaths(self, m, n):
if m == 0 or n == 0: return
ans = [[1] *n for _ in range(2)] # 模2
for i in range(1, m):
for j in range(1, n):
ans[i%2][j] = ans[i%2-1][j] + ans[i%2][j-1]
return ans[(m-1)%2][n-1]
4. Test cases
1) edge cases
2) 7, 3
[LeetCode] 62. Unique Paths_ Medium tag: Dynamic Programming的更多相关文章
- [LeetCode] 139. Word Break_ Medium tag: Dynamic Programming
Given a non-empty string s and a dictionary wordDict containing a list of non-empty words, determine ...
- [LeetCode] 55. Jump Game_ Medium tag: Dynamic Programming
Given an array of non-negative integers, you are initially positioned at the first index of the arra ...
- [LeetCode] 63. Unique Paths II_ Medium tag: Dynamic Programming
A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below). The ...
- [LeetCode] 64. Minimum Path Sum_Medium tag: Dynamic Programming
Given a m x n grid filled with non-negative numbers, find a path from top left to bottom right which ...
- [LeetCode] 152. Maximum Product Subarray_Medium tag: Dynamic Programming
Given an integer array nums, find the contiguous subarray within an array (containing at least one n ...
- [LeetCode] 97. Interleaving String_ Hard tag: Dynamic Programming
Given s1, s2, s3, find whether s3 is formed by the interleaving of s1 and s2. Example 1: Input: s1 = ...
- [LeetCode] 115. Distinct Subsequences_ Hard tag: Dynamic Programming
Given a string S and a string T, count the number of distinct subsequences of S which equals T. A su ...
- [LintCode] 77. Longest common subsequences_ Medium tag: Dynamic Programming
Given two strings, find the longest common subsequence (LCS). Example Example 1: Input: "ABCD&q ...
- [LeetCode] 70. Climbing Stairs_ Easy tag: Dynamic Programming
You are climbing a stair case. It takes n steps to reach to the top. Each time you can either climb ...
随机推荐
- 让Elasticsearch集群冷热分离、读写分离【转】
转自:https://blog.csdn.net/jiao_fuyou/article/details/50511255 根据Elasticsearch中文社区<ES冷热分离(读写分离) hot ...
- vue.js购物车
vue.js https://cn.vuejs.org/v2/guide/ 简单购物车 <html> <head> <script src="https://c ...
- (转)java术语(PO/POJO/VO/BO/DAO/DTO)
转自:http://blog.csdn.net/gaoyunpeng/article/details/2093211 PO(persistant object) 持久对象在o/r 映射的时候出现的概念 ...
- 以太坊客户端Geth命令用法-参数详解【转载】
原文链接:http://www.cnblogs.com/tinyxiong/p/7918706.html Geth在以太坊智能合约开发中最常用的工具(必备开发工具),一个多用途的命令行工具.熟悉Get ...
- c++的类的封装/继承/多态的简单介绍
本篇文章仅仅从很表层来介绍一个C++语言中的类,包括什么是类,类的封装性/继承性和多态性.高手直接跳过吧,看了浪费时间,新手或者想温习一下的可以浏览看看. 1. 什么是类? 到底什么是类(class) ...
- Easy UI combogrid动态加载数据
场景: datagrid的每一行允许编辑,一行中有一个字段,编辑时,提供下拉框选项,供选择. 下拉框选项有多个列.如下图所示:(点击红框内的下拉按钮,会弹出绿框内的内容) 要求: 每行弹出的下拉框内容 ...
- miniprogrampatch 提供 watch 和 computed 特性
推荐一个小程序补丁 github:miniprogrampatch,为你的 Page 和 Component 增加 watch 和 computed 特性. 安装 通过 npm 安装:npm inst ...
- timer计算两个方法执行时间
>>> from timeit import Timer >>> Timer("temp = x; x = y; y = temp", &quo ...
- win10下VS2017配置GSL库
GSL库:GNU Scientific Library 1. 下载:下载Complete package, except sources和Sources两个exe文件 2. 安装:将两个exe安装 ...
- nginx 报错 connect() failed (111: Connection refused) while connecting to upstream
公司网站搬迁到新服务器后,发现站点访问不了,network里面提示502,查看相关的server配置,感觉没有什么问题,经过测试发现txt.html.等非php文件能够直接访问,也就是php访问不了, ...