LeetCode_Unique Paths

A robot is located at the top-left corner of a m x n grid (marked 'Start' in the diagram below).

The robot can only move either down or right at any point in time. The robot is trying to reach the bottom-right corner of the grid (marked 'Finish' in the diagram below).

How many possible unique paths are there?

　　方法一： DFS 大数据超时

class Solution {
public:
    void DFS(int i, int j, int m, int n){
        if( i== m && j == n){
            result++;
        }
        if(j+ <= n) DFS(i, j+,m,n);
        if(i+ <= m) DFS(i+,j,m,n);
    }
    int uniquePaths(int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        result = ;
        DFS(,,m,n);
        return result;
    }
private:
 int result;
};

　　方法二：动态规划。 grid[i][j] = grid[i-1][j]+grid[i][j-1]

class Solution {
public:
    int uniquePaths(int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        vector<vector<int>> grid(m,vector<int>(n,));
        for(int i = ; i< n;i++) grid[][i] = ;
        for(int i = ; i< m;i++) grid[i][] = ;

        for(int i = ; i< m; i++)
            for(int j = ; j < n; j++)
                    grid[i][j] = grid[i-][j] + grid[i][j-];
        return grid[m-][n-] ;

    }
};