题目
Design a data structure that supports all following operations in average O(1) time.
- insert(val): Inserts an item val to the set if not already present.
- remove(val): Removes an item val from the set if present.
- getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.
解题思路
同时使用字典和列表，字典的key为给的值，val为其在list中的index，插入的时候同时插入到两个数据结构中，随机就直接在list中随机，删除则需要先将这个数与列表中的最后一个数交换，再删除
代码
class RandomizedSet:
def __init__(self):
"""
Initialize your data structure here.
"""
self.list = []
self.dic = {}
def insert(self, val: int) -> bool:
"""
Inserts a value to the set. Returns true if the set did not already contain the specified element.
"""
if val in self.dic:
return False
self.dic[val] = len(self.list)
self.list.append(val)
return True
def remove(self, val: int) -> bool:
"""
Removes a value from the set. Returns true if the set contained the specified element.
"""
if val not in self.dic:
return False
last, idx = self.list[-1], self.dic[val]
self.list[idx], self.dic[last] = last, idx
del self.list[-1]
del self.dic[val]
return True
def getRandom(self) -> int:
"""
Get a random element from the set.
"""
return random.choice(self.list)
