从昨天到现在，脑子真的很乱，基本不知道自己在干什么。
问题描述
Given a list of non negative integers, arrange them such that they form the largest number.
For example, given [3, 30, 34, 5, 9], the largest formed number is 9534330.
Note: The result may be very large, so you need to return a string instead of an integer.
问题分析
参考九章算法，即将原来的int数组转换为str数组后，比较任意两个x、y，如果x+y > y+x， 那么x应该放在y前面，这样就将这个问题变成了一个排序问题。
AC代码
class Solution:
# @param {integer[]} nums
# @return {string}
def largestNumber(self, nums):
strs = []
for i in nums:
strs.append(str(i))
strs = sorted(strs, cmp=lambda x,y: 1 if x+y < y+x else -1)
rst = ''.join(strs)
i = 0
while rst[0] == '0' and i < len(rst)-1:
i += 1
return rst[i:]
Runtime: 52 ms, which beats 90.00% of Python submissions.
语法知识点：sorted函数及lambda表达式。
