62. 不同路径

class Solution {
    public int uniquePaths(int m, int n) {
        // dp[i][j]: 从（0，0）到（i，j）有多少种不同的走法
        int[][] dp = new int[m][n];

        for(int i = 0; i < m; i++){
            dp[i][0] = 1;
        }
        for(int j = 0; j < n; j++){
            dp[0][j] = 1;
        }

        for(int i = 1; i < m; i++){
            for(int j = 1; j < n; j++){
                dp[i][j] = dp[i - 1][j] + dp[i][j - 1];
            }
        }

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

63. 不同路径 II

class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;

        // dp[i][j] ：表示从（0 ，0）出发，到(i, j) 有dp[i][j]条不同的路径。
        int[][] dp = new int[m][n];

        // 初始化
        for(int i = 0; i < m && obstacleGrid[i][0] == 0; i++)dp[i][0] = 1;
        for(int i = 0; i < n && obstacleGrid[0][i] == 0; i++)dp[0][i] = 1;

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

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