题目:有一个m * n 的方格,如下图,一个小robot希望从左上角走到右下角,共有多少种不同的路线走法. 思路: 我的错误思路:全排列,从(0,0)走到(m - 1,n - 1)共需要往下走m-1步,往右走n-1步.那么计算公式就是(全排列(m-1+n-1)/(全排列(m-1)*全排列(n-1))).想到这里我很happy的把全排列写好,submit, runtimeError.后面检测出是数值溢出了,即使使用long型数据接收全排列结果也会溢出.当然Java提供了BigInteger类帮助大…

Unique Paths II Total Accepted: 31019 Total Submissions: 110866My Submissions Question Solution  Follow up for "Unique Paths": Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty spa…

那么上述问题,假设这个矩阵堵塞障碍,不能在若干组合前面所用的方法,因为这么多的位置实际上是没有办法的事儿. 还有剩下的唯一合理的解决方案dp该.与最低要求,并且等,从右下角以前突起,对于位置(i, j),它的动作应该是(i+1, j)和(i, j+1)走法的和.对于边界条件还是有一些特殊,最后一行.从右往左,假设是0的话没有问题.等于右側走法的个数.一旦遇到一个1.那么它以及它左边的走法都必须置成0,你可没有穿墙术. 我认为题目明白说明了行列的个数,就是在暗示我们能够使用dp的方法,行列个数不大…

从左上到右下,仅仅能向右或向下,问一共同拥有多少种走法. 这个问题当然能够用递归和dp来做,递归的问题是非常可能会超时,dp的问题是须要额外空间. 事实上没有其它限制条件的话,这个问题有个非常easy的解法.给定一个格子.如果是m*n的.从左上角走到右下角的总步数是确定了的,(m+n-2)嘛,即在竖直方向一定要走m-1步.在水平方向一定要走n-1步.那有多少种解法就相当于确定什么时候往下走,什么时候往右走,也即相当于从这m+n-2步中.挑选出m-1步有多少种挑法,由于剩下的肯定要往右走嘛.问题实…

Follow up for "Unique Paths": Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space is marked as 1 and 0 respectively in the grid. For example, There is one obstacle in the middl…

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 t…

Title: https://leetcode.com/problems/unique-paths/ 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 bo…

Given a directed, acyclic graph of N nodes.  Find all possible paths from node 0 to node N-1, and return them in any order. The graph is given as follows:  the nodes are 0, 1, ..., graph.length - 1.  graph[i] is a list of all nodes j for which the ed…

原题地址:https://oj.leetcode.com/problems/unique-paths-ii/ 题意: Follow up for "Unique Paths": Now consider if some obstacles are added to the grids. How many unique paths would there be? An obstacle and empty space is marked as 1 and 0 respectively i…

原题地址:https://oj.leetcode.com/problems/unique-paths/ 题意: 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 t…