class Solution:
    def maximumSwap(self, num: int) -> int:

        #TC: O(len(num))
        #SC: O(1)

        List = [ele for ele in str(num)]
        Bucket = [-1] * 10 #the last position of the appearance of 0-9

        for i in range(len(List)):
            Bucket[int(List[i])] = i 

        for i in range(len(List)):
            ele = int(List[i])
            for j in range(9, ele, -1):
                if Bucket[j] > i:
                    List[i] = str(j)
                    List[Bucket[j]] = str(ele)

                    res = int(''.join(List))
                    return res
        return num