训练营第三十九天 | ● 62.不同路径 ● 63. 不同路径 II

class Solution {
    public int uniquePaths(int m, int n) {
        int[][] dp = new int[m][n];
        //初始化
        for(int i = 0; i < m; i++) dp[i][0] = 1;//最左
        for(int i = 0; i < n; i++) dp[0][i] = 1;//最上
        //遍历
        for(int i = 1; i < m; i++) {
            for(int j = 1; j < n; j++) {
                //递推公式
                dp[i][j] = dp[i][j-1] + dp[i-1][j];
            }
        }
        return dp[m-1][n-1];
    }
}

class Solution {
    public int uniquePathsWithObstacles(int[][] obstacleGrid) {
        int m = obstacleGrid.length;
        int n = obstacleGrid[0].length;
        int[][] dp = new int[m][n];
        //初始化 注意遇到障碍物就此路不通后面值为0
        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++) {
                //递推公式必须保证不是障碍物
                dp[i][j] = (obstacleGrid[i][j] == 0) ? dp[i-1][j] + dp[i][j-1] : 0;
            }
        }
        return dp[m-1][n-1];
    }
}

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