Unique paths

class Solution {
public:
    int countpath(int m,int n,int i,int j, vector<vector<int>> &dp)
    {

        if(i==m-1 && j==n-1)
        {
            return 1;
        }
        if(i==m || j==n)
        {
            return 0;
        }
        if(dp[i][j]!=0)
        {
            return dp[i][j];
        }
        return dp[i][j] = countpath(m,n,i+1,j,dp)+countpath(m,n,i,j+1,dp);
    }

    int uniquePaths(int m, int n) {
        vector<vector<int> > dp(m+1, vector<int>(n+1, 0));
        return countpath(m,n,0,0,dp);

    }
};