1class RunewordsCalculator:
 2    def __init__(self, runewords):
 3        self.runewords = list(runewords.items())
 4        self.runes = []
 5        self.used = set()
 6
 7    def add_runes(self, runes):
 8        self.runes.extend(runes)
 9
10    def __iter__(self):
11        return self
12
13    def __next__(self):
14        if len(self.used) == len(self.runewords):
15            raise StopIteration
16
17        for name, recipe in self.runewords:
18            if name in self.used:
19                continue
20
21            if self._consume_runes(recipe):
22                self.used.add(name)
23                return name
24
25        return None
26
27    def _consume_runes(self, recipe):
28        indices = []
29        recipe_index = 0
30        for i, rune in enumerate(self.runes):
31            if rune == recipe[recipe_index]:
32                indices.append(i)
33                recipe_index += 1
34
35                if recipe_index == len(recipe):
36                    break
37        if recipe_index < len(recipe):
38            return False
39
40        for i in reversed(indices): 
41            #not change indexing
42            self.runes.pop(i)
43
44        return True