I have saw many result with the usage if x+y and y+x, this cmp process need to load extra memory. my solution will request no extra memory in the compare process

```
class Solution:
# @param {integer[]} nums
# @return {string}
def numCmp(self,x,y):
xc, yc, xs, ys = 0, 0, len(x), len(y)
while True:
if ord(x[xc%xs]) == ord(y[yc%ys]):
xc += 1
yc += 1
if xc>len(x) and yc>len(y):
return 0
else:
return ord(x[xc%xs]) - ord(y[yc%ys])
def largestNumber(self, nums):
nums = [str(i) for i in nums]
nums.sort(cmp=self.numCmp, reverse=True)
return ''.join(nums).lstrip('0') or '0'
```