leetcode1288

 1 import itertools
 2 class CombinationIterator:
 3 
 4     def __init__(self, characters: str, combinationLength: int):
 5         self.lists = list(itertools.combinations(characters,combinationLength))
 6         self.index = 0
 7 
 8     def next(self) -> str:
 9         tp = self.lists[self.index]
10         self.index += 1
11         return ''.join(tp)
12 
13     def hasNext(self) -> bool:
14         return self.index < len(self.lists)

Itertools direct call built-in functions, to quickly generate qualified combinations.

1286. Iterator for Combination