UniquePaths

# 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(object):
    def uniquePaths(self, m, n):
        """
        :type m: int
        :type n: int
        :rtype: int
        """
        dp = []
        bottomLine = [1] * n
        dp.append(bottomLine)
        
        for i in range(m - 2 , -1, -1):
            currentLine = [0] * n
            currentLine[-1] = 1
            for j in range(n - 2, -1, -1):
                currentLine[j] = currentLine[j + 1] + dp[-1][j]
            dp.append(currentLine)
                
        return (dp[-1])[0]