Sort the array by two different concatenation situations first, then remember to check if `nums`

is empty or every elements in `nums`

are `0`

.

```
class Solution:
# @param {integer[]} nums
# @return {string}
def largestNumber(self, nums):
return "".join(sorted(map(str, nums), cmp = lambda x, y: cmp(y+x, x+y))) \
if nums and set(nums) != {0} else "0"
```