380. Insert Delete GetRandom O(1)-白红宇

380. Insert Delete GetRandom O(1)

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发布时间：2019-06-12

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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.

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 2 is the only number in the set, getRandom always return 2.randomSet.getRandom();

Approach #1: C++.

class RandomizedSet {public:    /** Initialize your data structure here. */    RandomizedSet() {            }        /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */    bool insert(int val) {        if (m.count(val)) return false;        m[val] = nums.size();        nums.push_back(val);        return true;    }        /** Removes a value from the set. Returns true if the set contained the specified element. */    bool remove(int val) {        if (!m.count(val)) return false;        int last = nums.back();        m[last] = m[val];        nums[m[val]] = last;        nums.pop_back();        m.erase(val);        return true;    }        /** Get a random element from the set. */    int getRandom() {        return nums[rand() % nums.size()];    }    private:    vector
      
        nums;    unordered_map
       
         m;};/** * Your RandomizedSet object will be instantiated and called as such: * RandomizedSet obj = new RandomizedSet(); * bool param_1 = obj.insert(val); * bool param_2 = obj.remove(val); * int param_3 = obj.getRandom(); */

Approach #2: Java.

class RandomizedSet {    ArrayList
     
       nums;    HashMap
      
        locs;    java.util.Random rand = new java.util.Random();    /** Initialize your data structure here. */    public RandomizedSet() {        nums = new ArrayList
       
        ();        locs = new HashMap
        
         ();    }        /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */    public boolean insert(int val) {        boolean contain = locs.containsKey(val);        if (contain) return false;        locs.put(val, nums.size());        nums.add(val);        return true;    }        /** Removes a value from the set. Returns true if the set contained the specified element. */    public boolean remove(int val) {        boolean contain = locs.containsKey(val);        if (!contain) return false;        int loc = locs.get(val);        if (loc < nums.size() - 1) {            int lastone = nums.get(nums.size() - 1);            nums.set(loc, lastone);            locs.put(lastone, loc);        }        locs.remove(val);        nums.remove(nums.size() - 1);        return true;    }        /** Get a random element from the set. */    public int getRandom() {        return nums.get(rand.nextInt(nums.size()));    }}/** * Your RandomizedSet object will be instantiated and called as such: * RandomizedSet obj = new RandomizedSet(); * boolean param_1 = obj.insert(val); * boolean param_2 = obj.remove(val); * int param_3 = obj.getRandom(); */

Approach #3: Python.

import randomclass RandomizedSet(object):    def __init__(self):        """        Initialize your data structure here.        """        self.nums, self.pos = [], {}            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 not in self.pos:            self.nums.append(val)            self.pos[val] = len(self.nums) - 1            return True        return False    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 in self.pos:            idx, last = self.pos[val], self.nums[-1]            self.nums[idx], self.pos[last] = last, idx            self.nums.pop(); self.pos.pop(val, 0)            return True        return False            def getRandom(self):        """        Get a random element from the set.        :rtype: int        """        return self.nums[random.randint(0, len(self.nums) - 1)]# 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()