【leetcode】949. Largest Time for Given Digits

题目如下：

Given an array of 4 digits, return the largest 24 hour time that can be made.

The smallest 24 hour time is 00:00, and the largest is 23:59.  Starting from 00:00, a time is larger if more time has elapsed since midnight.

Return the answer as a string of length 5.  If no valid time can be made, return an empty string.

Example 1:

Input: [1,2,3,4]
Output: "23:41"

Example 2:

Input: [5,5,5,5]
Output: ""

Note:

1. A.length == 4
2. 0 <= A[i] <= 9

解题思路：就四个数字，把所有组合方式列举一遍，求最大值即可。

代码如下：

class Solution(object):
    def largestTimeFromDigits(self, A):
        """
        :type A: List[int]
        :rtype: str
        """
        import itertools
        res = -1
        for i in itertools.permutations(A,4):
            if i[0]*10 + i[1] < 24 and i[2]*10 + i[3] < 60:
                res = max(res,(i[0]*1000+i[1]*100+i[2]*10+i[3]))
        if res == -1:
            return  ''
        res = str(res).zfill(4)
        return res[0:2] + ':' + res[2:]