减少循环次数参考:

def countSort(arr):
   count = [ 0 for i in range(256)]
   output = ["" for _ in arr]
   mx, mn = 0, 255
   for i in arr:
      idx = ord(i)
      if idx > mx: mx = idx
      if idx < mn: mn = idx
      count[idx] += 1
   idx = 0
   for i in range(mn, mx + 1):
      if count[i] == 0: continue
      for _ in range(count[i]):
         output[idx] = chr(i)
         idx += 1
   return output
arr = "wwwrunoobcom"
ans = countSort(arr) 
print ( "字符数组排序 %s"  %("".join(ans)) )