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?

Above is a 3 x 7 grid. How many possible unique paths are there?

answer:

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