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32 lines
974 B
Python
32 lines
974 B
Python
import random
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# https://stackoverflow.com/questions/15993447/python-data-structure-for-efficient-add-remove-and-random-choice
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class RandomizedSet:
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def __init__(self):
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self.store = []
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self.indices = {}
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def insert(self, val: int) -> bool:
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if val in self.indices:
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return False
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self.indices[val] = len(self.store)
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self.store.append(val)
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return True
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def remove(self, val: int) -> bool:
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if val not in self.indices:
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return False
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val_pos = self.indices.pop(val)
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last_val = self.store.pop()
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# if target was not at end, we popped something else
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# so overwrite target's position with it and update its pos
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# all O(1) operations
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if val_pos != len(self.store):
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self.store[val_pos] = last_val
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self.indices[last_val] = val_pos
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return True
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def getRandom(self) -> int:
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return random.choice(self.store)
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