标签：www. ecif array blog with param targe delete opera
Design a data structure that supports all following operations in average O(1) time.
Note: Duplicate elements are allowed.
insert(val): Inserts an item val to the collection.remove(val): Removes an item val from the collection if present.getRandom: Returns a random element from current collection of elements. The probability of each element being returned is linearly related to the number of same value the collection contains.
Example:
// Init an empty collection. RandomizedCollection collection = new RandomizedCollection(); // Inserts 1 to the collection. Returns true as the collection did not contain 1. collection.insert(1); // Inserts another 1 to the collection. Returns false as the collection contained 1. Collection now contains [1,1]. collection.insert(1); // Inserts 2 to the collection, returns true. Collection now contains [1,1,2]. collection.insert(2); // getRandom should return 1 with the probability 2/3, and returns 2 with the probability 1/3. collection.getRandom(); // Removes 1 from the collection, returns true. Collection now contains [1,2]. collection.remove(1); // getRandom should return 1 and 2 both equally likely. collection.getRandom();
380. Insert Delete GetRandom O(1) - Medium 的 follow-up
还是用hashmap和arraylist，hashmap中存<val, [val indices]>, arraylist中存 (val, index in hashmap)，即 (val, val在map.get(val)中对应的下标)
insert: 直接加在hash map对应的list末尾和arraylist的末尾
delete: 和最后一个元素交换，再删除最后一个元素。注意如果map.get(val)只有一个元素的时候，要把map中对应的val删除
class RandomizedCollection { Map<Integer, List<Integer>> map; List<int[]> list; Random r; /** Initialize your data structure here. */ public RandomizedCollection() { map = new HashMap<>(); list = new ArrayList<>(); r = new Random(); } /** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */ public boolean insert(int val) { if(map.containsKey(val)) { int idx = map.get(val).size() - 1; list.add(new int[] {val, idx + 1}); map.get(val).add(list.size() - 1); return false; } else { list.add(new int[] {val, 0}); map.put(val, new ArrayList<>()); map.get(val).add(list.size() - 1); return true; } } /** Removes a value from the collection. Returns true if the collection contained the specified element. */ public boolean remove(int val) { if(!map.containsKey(val)) { return false; } List<Integer> idxs = map.get(val); int idx = idxs.get(idxs.size() - 1); if(idxs.size() == 1) { int[] last = list.get(list.size() - 1); list.set(idx, last); list.remove(list.size() - 1); List<Integer> last_idxs = map.get(last[0]); last_idxs.set(last[1], idx); map.remove(val); return true; } if(idx < list.size() - 1) { int[] last = list.get(list.size() - 1); list.set(idx, last); List<Integer> last_idxs = map.get(last[0]); last_idxs.set(last[1], idx); } list.remove(list.size() - 1); List<Integer> tmp = map.get(val); tmp.remove(tmp.size() - 1); return true; } /** Get a random element from the collection. */ public int getRandom() { return list.get(r.nextInt(list.size()))[0]; } } /** * Your RandomizedCollection object will be instantiated and called as such: * RandomizedCollection obj = new RandomizedCollection(); * boolean param_1 = obj.insert(val); * boolean param_2 = obj.remove(val); * int param_3 = obj.getRandom(); */
381. Insert Delete GetRandom O(1) - Duplicates allowed - Hard
标签：www. ecif array blog with param targe delete opera
原文地址：https://www.cnblogs.com/fatttcat/p/10214480.html
