Unique Paths

Source

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?

Note
m and n will be at most 100.

Python

class Solution:
    """
    @param n and m: positive integer(1 <= n , m <= 100)
    @return an integer
    """ 
    def uniquePaths(self, m, n):
        # write your code here
        row=[0]*m
        row[0]=1

        for i in range(n):
            for j in range(1, m):
                row[j]+=row[j-1]

        return row[m-1]