LeetCode每日一题：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 as1and0respectively 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 is2.
Note: m and n will be at most 100.

问题分析

跟前一题类似，只要记住若该点为1，则到达该点的方法数为0

if (obstacleGrid[i][j] == 1) dp[i][j] = 0;
else dp[i][j] = dp[i - 1][j] + dp[i][j - 1];

代码实现

public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;
        int[][] dp = new int[m][n];
        for (int i = 0; i < m; i++) {
            if (obstacleGrid[i][0] == 1) break;
            else dp[i][0] = 1;
        }
        for (int i = 0; i < n; i++) {
            if (obstacleGrid[0][i] == 1) break;
            else dp[0][i] = 1;
        }
        for (int i = 1; i < m; i++) {
            for (int j = 1; j < n; j++) {
                if (obstacleGrid[i][j] == 1) dp[i][j] = 0;
                else dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
            }
        }
        return dp[m - 1][n - 1];
    }