Unique Paths

There is a robot on an m x n grid. The robot is initially located at the top-left corner (i.e., grid[0][0]). The robot tries to move to the bottom-right corner (i.e., grid[m - 1][n - 1]). The robot can only move either down or right at any point in time.

Given the two integers m and n, return the number of possible unique paths that the robot can take to reach the bottom-right corner.

class Solution:
    def uniquePaths(self, m, n):
        dp = [[1]*n for i in range(m)]
        for i, j in product(range(1, m), range(1, n)):
            dp[i][j] = dp[i-1][j] + dp[i][j-1]
        return dp[-1][-1]