1class RunewordsCalculator:
 2    def __init__(self, runewords):
 3        self.runewords = list(runewords.items())
 4        self.runes = []
 5        self.returned = 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.returned) == len(self.runewords):
15            raise StopIteration
16        for name, recipe in self.runewords:
17            if name in self.returned:
18                continue
19            indexes = self._find_indexes(recipe)
20            if indexes is not None:
21                self._delete_indexes(indexes)
22                self.returned.add(name)
23                return name
24        return None
25        
26    def _find_indexes(self, recipe):
27        indexes = []
28        recipe_index = 0
29        for rune_index, rune in enumerate(self.runes):
30            if rune == recipe[recipe_index]:
31                indexes.append(rune_index)
32                recipe_index += 1
33                if recipe_index == len(recipe):
34                    return indexes
35        return None
36
37    def _delete_indexes(self, indexes):
38        for rune_index in reversed(indexes):
39            self.runes.pop(rune_index)