代码随想录算法训练营Day40 | 62.不同路径 63. 不同路径 II

代码随想录算法训练营Day40 | 62.不同路径 63. 不同路径 II

LeetCode 62.不同路径

题目链接：LeetCode 62.不同路径

思路：
二维数组dp，简单

class Solution {
public:
    int uniquePaths(int m, int n) {
        if( m==1 || n==1 ) return 1;
        vector<vector<int>> dp(m,vector<int>(n,0));
        dp[0][0] = 1;
        for(int i = 1; i<m; i++ ){
            for(int j = 1; j<n; j++ ){
                if(i == 1){
                    dp[i-1][j] = 1;
                }
                if(j == 1){
                    dp[i][j-1] = 1;
                }
                dp[i][j] = dp[i-1][j] + dp[i][j-1];
            }
        }
        return dp[m-1][n-1];
    }
};

LeetCode 63. 不同路径 II

题目链接：LeetCode 63. 不同路径 II

思路：
分4种情况，写法需要优化

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int>>& obstacleGrid) {
        int m = obstacleGrid.size();
        int n = obstacleGrid[0].size();
        vector<vector<int>> dp(m, vector<int>(n, 0));
        if (obstacleGrid[0][0]) return 0;
        dp[0][0] = 1;
        for(int i=1; i<m; i++){
            if (obstacleGrid[i][0] == 1){
                for(; i<m; i++) dp[i][0] = 0;
            }
            else dp[i][0] = 1;
        }
        for(int j=1; j<n; j++){
            if (obstacleGrid[0][j] == 1){
                for(; j<n; j++) dp[0][j] = 0;
            }
            else dp[0][j] = 1;
        }

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