63. Unique Paths II

    /*
     * 63. Unique Paths II
     * 12.20 by Mingyang
     * 这里是二维DP，需要注意的是i是从1到m，j是从1到n，这里i与j没有联系。
     * 然后二维的n m分别是长与宽
     */
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;
        if (m == 0 || n == 0)
            return 0;
        if (obstacleGrid[0][0] == 1 || obstacleGrid[m - 1][n - 1] == 1)
            return 0;
        int[][] dp = new int[m][n];
        dp[0][0] = 1;
        for (int i = 1; i < n; i++) {
            if (obstacleGrid[0][i] == 1)
                dp[0][i] = 0;
            else
                dp[0][i] = dp[0][i - 1];
        }
        for (int i = 1; i < m; i++) {
            if (obstacleGrid[i][0] == 1)
                dp[i][0] = 0;
            else
                dp[i][0] = dp[i - 1][0];
        }
        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][j - 1] + dp[i - 1][j];
            }
        }
        return dp[m - 1][n - 1];
    }