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?

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

Note: m and n will be at most 100.

class Solution {
public:
    int uniquePaths(int m, int n) {
        // Start typing your C/C++ solution below
        // DO NOT write int main() function
        if (m == 0 || n == 0) {
            return 0;
        }
        int A[m][n];
        A[0][0] = 1;
        for (int i = 0; i < m; ++i) {
            for (int j = 0; j < n; ++j) {
                if (i == 0 && j > 0) {
                    A[i][j] = A[i][j-1];
                }
                if (j == 0 && i > 0) {
                    A[i][j] = A[i-1][j];
                }
                if (i > 0 && j > 0) {
                    A[i][j] = A[i][j-1] + A[i-1][j];
                }
            }
        }
        return A[m-1][n-1];
    }
};