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();
public class RandomizedSet {HashMap<Integer, Integer> map = new HashMap<Integer, Integer>();ArrayList<Integer> al = new ArrayList<Integer>();Random rand = new Random(); /** Initialize your data structure here. */ public RandomizedSet() { } /** Inserts a value to the set. Returns true if the set did not already contain the specified element. */ public boolean insert(int val) { if(map.containsKey(val)) return false; map.put(val, map.size()); al.add(val); return true; } /** Removes a value from the set. Returns true if the set contained the specified element. */ public boolean remove(int val) { if(!map.containsKey(val)) return false; int loc = map.get(val); if(loc != al.size()-1){ int last = al.get(al.size()-1); al.set(loc, last); map.put(last, loc); } map.remove(val); al.remove(al.size()-1); return true; } /** Get a random element from the set. */ public int getRandom() { return al.get(rand.nextInt(al.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(); */新闻热点
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