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?

int uniquePaths(int m, int n) {  if (m == 1 || n == 1) return 1;  vector<vector<int> > dmatrix(m + 1, vector<int>(n + 1, 0));  dmatrix[0][1] = 1;  for (int i = 1; i <= m; i++)  {    for (int j = 1; j <= n; j++)    {      dmatrix[i][j] = dmatrix[i - 1][j] + dmatrix[i][j - 1];    }  }  return dmatrix[m][n];}