380.Insert Delete GetRandom O(1)

tags: Medium,Array,Hash Table,Math

380. Insert Delete GetRandom O(1)

題目描述

Implement the RandomizedSet class:

• RandomizedSet() Initializes the RandomizedSet object.
• bool insert(int val) Inserts an item val into the set if not present. Returns true if the item was not present, false otherwise.
• bool remove(int val) Removes an item val from the set if present. Returns true if the item was present, false otherwise.
• int getRandom() Returns a random element from the current set of elements (it's guaranteed that at least one element exists when this method is called). Each element must have the same probability of being returned.

You must implement the functions of the class such that each function works in average

$O(1)$ time complexity.

範例

Example 1:

Input
["RandomizedSet", "insert", "remove", "insert", "getRandom", "remove", "insert", "getRandom"]
[[], [1], [2], [2], [], [1], [2], []]
Output
[null, true, false, true, 2, true, false, 2]

Explanation
RandomizedSet randomizedSet = new RandomizedSet();
randomizedSet.insert(1); 
// Inserts 1 to the set. Returns true as 1 was inserted successfully.

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

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

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

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

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

randomizedSet.getRandom(); 
// Since 2 is the only number in the set, getRandom() will always return 2.

Constraints:

• $-2^{31}$ <= val <=
  $2^{31}-1$
• At most
  $2\ast {10}^5$ calls will be made to insert, remove, and getRandom.
• There will be at least one element in the data structure when getRandom is called.

解答

Python

from random import randint
class RandomizedSet:

    def __init__(self):
        self.ht = defaultdict(bool)
        self.set = set()

    def insert(self, val: int) -> bool:
        if not self.ht[val]:
            self.ht[val] = True
            self.set.add(val)
            return True
        return False
    
    def remove(self, val: int) -> bool:
        if self.ht[val]:
            self.ht[val] = False
            self.set.remove(val)
            return True
        return False

    def getRandom(self) -> int:
        choose = randint(0, len(self.set) - 1)
        return list(self.set)[choose]

# 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()

KobeTue, Nov 29

class RandomizedSet:

    def __init__(self):
        self.data = set()

    def insert(self, val: int) -> bool:
        if val in self.data:
            return False
        self.data.add(val)
        return True

    def remove(self, val: int) -> bool:
        if val not in self.data:
            return False
        self.data.remove(val)
        return True

    def getRandom(self) -> int:
        return sample(self.data, 1)[0]

Yen-Chi ChenTue, Nov 29, 2022

C++

class RandomizedSet {
    vector<int> data;
    unordered_map<int, int> m;
public:
    RandomizedSet() {
        
    }
    
    bool insert(int val) {
        if (m.find(val) != m.end()) {
            return false;
        }
        m[val] = data.size();
        data.push_back(val);
        return true;
    }
    
    bool remove(int val) {
        if (m.find(val) != m.end()) {
            data[m[val]] = data.back();
            m[data.back()] = m[val];
            data.pop_back();
            m.erase(val);
            return true;
        }
        return false;
    }
    
    int getRandom() {
        return data[rand() % data.size()];
    }
};

Yen-Chi ChenTue, Nov 29, 2022

Javascript

class RandomizedSet {
  constructor() {
    this.map = new Map();
    this.list = [];
  }

  insert(val) {
    if (this.map.has(val)) return false;
    this.map.set(val, this.list.length);
    this.list.push(val);
    return true;
  }

  remove(val) {
    if (!this.map.has(val)) return false;
    const index = this.map.get(val);
    const last = this.list.pop();
    if (index !== this.list.length) {
      this.list[index] = last;
      this.map.set(last, index);
    }
    this.map.delete(val);
    return true;
  }

  getRandom() {
    return this.list[~~(Math.random() * this.list.length)];
  }
}

MarsgoatNov 29, 2022

Reference

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