179. Largest Number（sort中比较规则的用法）

Given a list of non negative integers, arrange them such that they form the largest number.

Example 1:

Input: [10,2]
Output: "210"

Example 2:

Input: [3,30,34,5,9]
Output: "9534330"

Note: The result may be very large, so you need to return a string instead of an integer.

class compare(str):
    def __lt__(a, b):
        return a + b >b + a

class Solution(object):
    def largestNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: str
        """
        res = ''.join(sorted(map(str,nums),key = compare))
        return '0' if res[0]=='0' else res

konw how to use compare and map