LeetCode63 Unique Paths II

Unique Paths II

问题描述

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 middle of a 3x3 grid as illustrated below.

[  [0,0,0],  [0,1,0],  [0,0,0]]

The total number of unique paths is 2.

Note: m and n will be at most 100.

简单分析

这道题和之前的一道题LeetCode62 Unique Paths是相同的，只是在一些位置加入了障碍，这些障碍会减少可以通过的路径。算法基本和之前的是一样的，也是采用动态规划的方法，但是有一点不同的是，如果出现障碍，那么这个位置的可行解为0.

代码如下

public int uniquePathsWithObstacles(int[][] obstacleGrid) {    int n = obstacleGrid[0].length;    int[]dp = new int[n];    //计算第一行    dp[0]=1;    //计算其余行    for (int i = 0; i < obstacleGrid.length; i++) {        for (int j = 0; j < n; j++) {            if(obstacleGrid[i][j]==1){                dp[j]=0;            }else if(j>0){                dp[j]+=dp[j-1];            }        }    }    return dp[n-1];}

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