最大交换

def solve(____):
    digits = list(str(int(____)))
    n = len(____)
    last = {d: i for i, d in enumerate(____)}
    for i in range(____):
        for d in '____':
            if d <= digits[i]: continue
            if last.get(____) > i:
                j = last[d]
                digits[i], digits[j] = digits[j], digits[i]
                print(int('____'.join(____)))
                return
    print(int('____'.join(____)))