Unique Paths

Q:
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?

Note: m and n will be at most 100.

T:
DP.

A:

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