62.不同路径

class Solution {
public:
    int uniquePaths(int m, int n) {
        // dp[i][j] 表示在这个位置共有多少种路径
        // dp[i][j] = dp[i-1][j] + dp[i][j-1]
        // dp[i][0] == dp[0][j] == 1

        vector<vector<int>> dp(m, vector<int>(n, 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(vector<vector<int>>& obstacleGrid) {
        // dp[i][j]表示共有多少种路径
        // dp[i][j] = dp[i-1][j] + dp[i][j-1]

        int m = obstacleGrid.size();
        int n = obstacleGrid[0].size();
        vector<vector<int>> dp(m, vector<int>(n, 0));
        for (int i = 0; i < m; i++) {
            if (obstacleGrid[i][0] == 0) {
                dp[i][0] = 1;
            } else break;
        }
        for (int j = 0; j < n; j++) {
            if (obstacleGrid[0][j] == 0) {
                dp[0][j] = 1;
            } else break;
        }

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