[LeetCode] 670. Maximum Swap

 Problem : https://leetcode.com/problems/maximum-swap/

To get maximum value, we need to have the larger digits on the higher end.

class Solution:
    def maximumSwap(self, num: int) -> int:
        digits = []
        
        # get digits
        while num:
            digits.append(num % 10)
            num = num // 10
        
        digits = digits[::-1]
        
        # find the max digits on right of each position
        N = len(digits)
        mxFromRight = [0] * N
        
        mxFromRight[N-1] = N-1
        mxForNow = N-1
        
        for i in reversed(range(N)):
            if digits[mxForNow] < digits[i]:
                mxForNow = i
            
            mxFromRight[i] = mxForNow
        
        for i in range(N):
            # iterate from left and swap the first digit not equal to the maximum digit from right side.
            if digits[i] == digits[mxFromRight[i]] :
                continue
            
            digits[i], digits[mxFromRight[i]] =  digits[mxFromRight[i]],  digits[i]
            break
        
        # assemble the final result
        result = 0
        for i in range(N):
            result = result * 10
            result += digits[i]
        
        return result