leetcode Insert Delete GetRandom O(1)

leetcode Insert Delete GetRandom O(1)

Design a data structure that supports all following operations in O(1) time.

  1. insert(val): Inserts an item val to the set if not already present.
  2. remove(val): Removes an item val from the set if present.
  3. getRandom: Returns a random element from current set of elements. Each element must have the same probability of being returned.


// Init an empty set.
RandomizedSet randomSet = new RandomizedSet();

// Inserts 1 to the set. Returns true as 1 was inserted successfully.

// Returns false as 2 does not exist in the set.

// Inserts 2 to the set, returns true. Set now contains [1,2].

// getRandom should return either 1 or 2 randomly.

// Removes 1 from the set, returns true. Set now contains [2].

// 2 was already in the set, so return false.

// Since 1 is the only number in the set, getRandom always return 1.

题目地址:leetcode Insert Delete GetRandom O(1)

题目大意: 要求实现一个数据结构,可以支持插入,删除,随机数生成。 他们的复杂度均要求O(1)

思路:用hash记录下标, 删除只需要和末尾元素调换即可

ps :无聊身边没电脑用手机1A了此题。。。还发了blog

import random
class RandomizedSet(object):

    def __init__(self):
        Initialize your data structure here.
        self.output = []
        self.index = {}

    def insert(self, val):
        Inserts a value to the set. Returns true if the set did not already contain the specified element.
        :type val: int
        :rtype: bool
        if val in self.index:
            return False
        self.index[val] = len(self.output)
        return True

    def remove(self, val):
        Removes a value from the set. Returns true if the set contained the specified element.
        :type val: int
        :rtype: bool
        if val not in self.index:
            return False
        index = self.index[val]
        self.index[last] = index
        self.output[index] = last
        del self.index[val]
        return True

    def getRandom(self):
        Get a random element from the set.
        :rtype: int
        index = random.randint(0,len(self.output)-1)
        return self.output[index]

# Your RandomizedSet object will be instantiated and called as such:
# obj = RandomizedSet()
# param_1 = obj.insert(val)
# param_2 = obj.remove(val)
# param_3 = obj.getRandom()


本题是leetcode 380 Insert Delete GetRandom O(1)的题解


本博客若无特殊说明则由 hrwhisper 原创发布
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