Leetcode Unique Paths

class Solution:
    def uniquePaths(self, m: int, n: int) -> int:
        
        '''
        Normal 2 ways poss. everytime
        Once you reach max height only 1 route possible then(but this is already counted above)
     Robot needs to take 2+6 = 8 steps with 2 down and 6 right in any order. That is nothing but a permutation      problem. Denote down as 'D' and right as 'R', following is one of the path :-

    (7*3)   ===   D R R R D R R R
        
        (3*3)
        R D R D
        _ _ _ _ 
        
        (m+n)!//m!*n!  ==> Due to total ways of placing m obj in n places(m+n)!  . M duplicates and N duplicates
        
        '''
        
        #Actual Code
        
        a=1
        target_x = n-1
        target_y = m-1
        num = target_x + target_y
        def fact(x):
            if x==1:
                return x
            if x<1:
                return 1
            else:
                return x*fact(x-1)
        num_fact = fact(num)
        num_den1 = fact(target_x)
        num_den2 = fact(target_y)
        
        
        out = int(num_fact/(num_den1*num_den2))
        return out