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Copy pathinsert_remove_getRandom.py
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80 lines (65 loc) · 2.53 KB
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'''
Design a data structure that supports all following operations in average O(1) time.
Note: Duplicate elements are allowed.
insert(val): Inserts an item val to the collection.
remove(val): Removes an item val from the collection if present.
getRandom: Returns a random element from current collection of elements. The probability of each element being returned is linearly related to the number of same value the collection contains.
Example:
// Init an empty collection.
RandomizedCollection collection = new RandomizedCollection();
// Inserts 1 to the collection. Returns true as the collection did not contain 1.
collection.insert(1);
// Inserts another 1 to the collection. Returns false as the collection contained 1. Collection now contains [1,1].
collection.insert(1);
// Inserts 2 to the collection, returns true. Collection now contains [1,1,2].
collection.insert(2);
// getRandom should return 1 with the probability 2/3, and returns 2 with the probability 1/3.
collection.getRandom();
// Removes 1 from the collection, returns true. Collection now contains [1,2].
collection.remove(1);
// getRandom should return 1 and 2 both equally likely.
collection.getRandom();
'''
class RandomizedCollection(object):
def __init__(self):
import collections
self.vals = list()
self.idxs = collections.defaultdict(set)
def insert(self, val):
self.vals.append(val)
self.idxs[val].add(len(self.vals) - 1)
return len(self.idxs[val]) == 1
def remove(self, val):
if self.idxs[val]:
out = self.idxs[val].pop()
ins = self.vals[-1]
self.vals[out] = ins
if self.idxs[ins]:
self.idxs[ins].add(out)
self.idxs[ins].remove(len(self.vals) - 1)
self.vals.pop()
return True
return False
def getRandom(self):
import random
return random.choice(self.vals)
# Your RandomizedCollection object will be instantiated and called as such:
#["RandomizedCollection","insert","insert","insert","insert","insert","remove","remove","remove","getRandom","getRandom","getRandom","getRandom"]
[[],[0],[1],[2],[3],[3],[2],[3],[0],[],[],[],[]]
obj = RandomizedCollection()
print obj.insert(0)
print obj.insert(1)
print obj.insert(2)
print obj.insert(3)
print obj.insert(3)
print obj.remove(2)
print obj.remove(3)
print obj.remove(0)
print obj.getRandom()
print obj.getRandom()
print obj.getRandom()
print obj.getRandom()
obj2 = RandomizedCollection()
print obj2.insert(1)
print obj2.remove(1)
print obj2.insert(1)