代码随想录day34：动态规划part2

文章目录

• • day34：动态规划part2
  • • 62.不同路径
    • [63.不同路径 II](#63.不同路径 II)

day34：动态规划part2

62.不同路径

class Solution {
    public int uniquePaths(int m, int n) {
        // dp[i][j]：到达(i, j)的路径数量
        int[][] dp = new int[m][n];
        for (int j = 0; j < n; j++) dp[0][j] = 1;
        for (int i = 1; i < m; i++) dp[i][0] = 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;
        int[][] dp = new int[m][n];
        for (int j = 0; j < n && obstacleGrid[0][j] == 0; j++) dp[0][j] = 1;
        // 都从0开始，防止起点有障碍物的情况
        for (int i = 0; i < m && obstacleGrid[i][0] == 0; i++) dp[i][0] = 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];
        return dp[m - 1][n - 1];
    }
}