Unique Paths

最新推荐文章于 2025-08-19 00:15:00 发布

原创最新推荐文章于 2025-08-19 00:15:00 发布 · 477 阅读

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class Solution {
public:
    long long pailei(int m) {
        long long res=1;
        int i=m;
        while (i>0) {
            res *=i;
            i--;
        }
        return res;
    }
    int uniquePaths(int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        long long res=pailei(m+n-2)/pailei(m-1)/pailei(n-1);
        
        return res;
    }
};

A little bit improved, but still cannot pass the large judge

class Solution {
public:
    long long pailei(int m, int n) {
        long long res=1;
        int i=m;
        while (i>n) {
            res *=i;
            i--;
        }
        return res;
    }
    int uniquePaths(int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        long long res=pailei(m+n-2,m-1)/pailei(n-1,0);
        
        return res;
    }
};

use DP

class Solution {
public:
    int uniquePaths(int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int res[m][n];
        for (int i=0; i<m; i++) {
            res[i][n-1]=1;
        }
        for (int i=0; i<n; i++) {
            res[m-1][i]=1;
        }
        for (int i=m-2; i>=0; i--) {
            for (int j=n-2; j>=0; j--) {
                res[i][j]=res[i][j+1]+res[i+1][j];
            }
        }        
        return res[0][0];
    }
};

DFS：

class Solution {
public:
    void dfs(vector<vector<int> > &obstacleGrid, int &res, int x, int y) {
        if (x>obstacleGrid.size()-1 || y>obstacleGrid[0].size()-1) return;
        if (obstacleGrid[x][y]==1) return;
        if (x==obstacleGrid.size()-1 && y==obstacleGrid[0].size()-1) {
            res++;
            return;
        }
        dfs(obstacleGrid, res, x, y+1);
        dfs(obstacleGrid, res, x+1, y);
    }
    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {
        if (obstacleGrid.size()==0) return 0;
        int res=0;
        dfs(obstacleGrid, res, 0, 0);
        return res;
    }
};

好吧，递归会超时

class Solution {
public:
    int uniquePathsWithObstacles(vector<vector<int> > &obstacleGrid) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        int m=obstacleGrid.size();
        int n=obstacleGrid[0].size();
        int res[m][n];
        if (obstacleGrid[m-1][n-1]==1) return 0;
        else res[m-1][n-1]=1;
        for (int i=m-2; i>=0; i--) {  
            if (obstacleGrid[i][n-1]==1) {
                res[i][n-1]=0;
            }else {
                res[i][n-1]=res[i+1][n-1];
            }
        }  
        for (int i=n-2; i>=0; i--) {
            if (obstacleGrid[m-1][i]==1) {
                res[m-1][i]=0;
            }else {
                res[m-1][i]=res[m-1][i+1];
            }
              
        }  
        for (int i=m-2; i>=0; i--) {  
            for (int j=n-2; j>=0; j--) {
                if (obstacleGrid[i][j]==1) {
                    res[i][j]=0;
                }else {
                    res[i][j]=res[i][j+1]+res[i+1][j];
                }
                  
            }  
        }          
        return res[0][0]; 
    }
};

14/2/17:

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