题目描述

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 3×3 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.

分析

参考LeetCode 062 Unique Paths

有障碍物的时候（obstacleGrid[i][j]==1），将对应的dp置0（dp[i][j]=0）。

代码

    public static int uniquePathsWithObstacles(int[][] obstacleGrid) {

        if (obstacleGrid == null || obstacleGrid[0] == null) {
            return 0;
        }

        if (obstacleGrid[0][0]==1) {
            return 0;
        }

        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;

        int[][] dp = new int[m][n];

        for (int y = 1; y < n; y++) {
            if (obstacleGrid[0][y] == 0) {
                dp[0][y] = 1;
            } else {
                break;
            }
        }

        for (int x = 0; x < m; x++) {
            if (obstacleGrid[x][0] == 0) {
                dp[x][0] = 1;
            } else {
                break;
            }
        }

        for (int y = 1; y < n; y++) {
            for (int x = 1; x < m; x++) {
                if (obstacleGrid[x][y] == 1) {
                    dp[x][y] = 0;
                } else {
                    dp[x][y] = dp[x - 1][y] + dp[x][y - 1];
                }

            }
        }

        return dp[m-1][n-1];
    }