leetcode 之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?

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