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.

Example:

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

// Inserts 1 to the set. Returns true as 1 was inserted successfully.
randomSet.insert(1);

// Returns false as 2 does not exist in the set.
randomSet.remove(2);

// Inserts 2 to the set, returns true. Set now contains [1,2].
randomSet.insert(2);

// getRandom should return either 1 or 2 randomly.
randomSet.getRandom();

// Removes 1 from the set, returns true. Set now contains [2].
randomSet.remove(1);

// 2 was already in the set, so return false.
randomSet.insert(2);

// Since 1 is the only number in the set, getRandom always return 1.
randomSet.getRandom();

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)
        self.output.append(val)
        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]
        last=self.output[-1]
        self.index[last] = index
        self.output[index] = last
        self.output.pop()
        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

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