[LeetCode] 381. Insert Delete GetRandom O(1) - Duplicates allowed 插入删除和获得随机数O(1)时间 - 允许重复

Design a data structure that supports all following operations in average O(1) time.

Note: Duplicate elements are allowed.

 

1. insert(val): Inserts an item val to the collection.
2. remove(val): Removes an item val from the collection if present.
3. 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)的拓展，这题是可以有重复数字。只需将上一题目的解法稍作改动，依然使用哈希表+数组，这次哈希表中的值是保存数组下标的一个Set。

Java：

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import java.util.ArrayList; import java.util.HashMap; import java.util.Random; import java.util.TreeSet;   public class RandomizedCollection {       private HashMap<Integer, TreeSet<Integer>> dataMap;     private ArrayList<Integer> dataList;      /** Initialize your data structure here. */     public RandomizedCollection() {         dataMap = new HashMap<Integer, TreeSet<Integer>>();         dataList = new ArrayList<Integer>();     }           /** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */     public boolean insert(int val) {         TreeSet<Integer> idxSet = dataMap.get(val);         if (idxSet == null) {             idxSet = new TreeSet<Integer>();             dataMap.put(val, idxSet);         }         idxSet.add(dataList.size());         dataList.add(val);         return idxSet.size() == 1;     }           /** Removes a value from the collection. Returns true if the collection contained the specified element. */     public boolean remove(int val) {         TreeSet<Integer> idxSet = dataMap.get(val);         if (idxSet == null || idxSet.isEmpty()) {             return false;         }         int idx = idxSet.pollLast(); //Last index of val         int tail = dataList.get(dataList.size() - 1); //Tail of list         TreeSet<Integer> tailIdxSet = dataMap.get(tail);         if (tail != val) {             tailIdxSet.pollLast(); //Remove last idx of list tail             tailIdxSet.add(idx); //Add idx to tail idx set             dataList.set(idx, tail);         }         dataList.remove(dataList.size() - 1);         return true;     }           /** Get a random element from the collection. */     public int getRandom() {         return dataList.get(new Random().nextInt(dataList.size()));     } }

Python:

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from random import randint from collections import defaultdict   class RandomizedCollection(object):       def __init__(self):         """         Initialize your data structure here.         """         self.__list = []         self.__used = defaultdict(list)                 def insert(self, val):         """         Inserts a value to the collection. Returns true if the collection did not already contain the specified element.         :type val: int         :rtype: bool         """         has = val in self.__used           self.__list += val,         self.__used[val] += len(self.__list)-1,           return not has         def remove(self, val):         """         Removes a value from the collection. Returns true if the collection contained the specified element.         :type val: int         :rtype: bool         """         if val not in self.__used:             return False           self.__used[self.__list[-1]][-1] = self.__used[val][-1]         self.__list[self.__used[val][-1]], self.__list[-1] = self.__list[-1], self.__list[self.__used[val][-1]]           self.__used[val].pop()         if not self.__used[val]:             self.__used.pop(val)         self.__list.pop()           return True       def getRandom(self):         """         Get a random element from the collection.         :rtype: int         """         return self.__list[randint(0, len(self.__list)-1)]

C++:

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class RandomizedCollection { public:     /** Initialize your data structure here. */     RandomizedCollection() {}           /** Inserts a value to the collection. Returns true if the collection did not already contain the specified element. */     bool insert(int val) {         m[val].insert(nums.size());         nums.push_back(val);         return m[val].size() == 1;     }           /** Removes a value from the collection. Returns true if the collection contained the specified element. */     bool remove(int val) {         if (m[val].empty()) return false;         int idx = *m[val].begin();         m[val].erase(idx);         if (nums.size() - 1 != idx) {             int t = nums.back();             nums[idx] = t;             m[t].erase(nums.size() - 1);             m[t].insert(idx);         }         nums.pop_back();         return true;     }           /** Get a random element from the collection. */     int getRandom() {         return nums[rand() % nums.size()];     }   private:     vector<int> nums;     unordered_map<int, unordered_set<int>> m; };

　　

 

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[LeetCode] 380. Insert Delete GetRandom O(1) 插入删除获得随机数O(1)时间

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