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)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:
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:
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++:
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;
};
类似题目:
[LeetCode] 380. Insert Delete GetRandom O(1) 插入删除获得随机数O(1)时间
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