一、题目

Design a data structure that keeps track of the values in it and answers some queries regarding their frequencies.

Implement the FrequencyTracker class.

FrequencyTracker(): Initializes the FrequencyTracker object with an empty array initially.
void add(int number): Adds number to the data structure.
void deleteOne(int number): Deletes one occurrence of number from the data structure. The data structure may not contain number, and in this case nothing is deleted.
bool hasFrequency(int frequency): Returns true if there is a number in the data structure that occurs frequency number of times, otherwise, it returns false.

Example 1:

Input
[“FrequencyTracker”, “add”, “add”, “hasFrequency”]
[[], [3], [3], [2]]
Output
[null, null, null, true]

Explanation
FrequencyTracker frequencyTracker = new FrequencyTracker();
frequencyTracker.add(3); // The data structure now contains [3]
frequencyTracker.add(3); // The data structure now contains [3, 3]
frequencyTracker.hasFrequency(2); // Returns true, because 3 occurs twice

Example 2:

Input
[“FrequencyTracker”, “add”, “deleteOne”, “hasFrequency”]
[[], [1], [1], [1]]
Output
[null, null, null, false]

Explanation
FrequencyTracker frequencyTracker = new FrequencyTracker();
frequencyTracker.add(1); // The data structure now contains [1]
frequencyTracker.deleteOne(1); // The data structure becomes empty []
frequencyTracker.hasFrequency(1); // Returns false, because the data structure is empty

Example 3:

Input
[“FrequencyTracker”, “hasFrequency”, “add”, “hasFrequency”]
[[], [2], [3], [1]]
Output
[null, false, null, true]

Explanation
FrequencyTracker frequencyTracker = new FrequencyTracker();
frequencyTracker.hasFrequency(2); // Returns false, because the data structure is empty
frequencyTracker.add(3); // The data structure now contains [3]
frequencyTracker.hasFrequency(1); // Returns true, because 3 occurs once

Constraints:

1 <= number <= 105
1 <= frequency <= 105
At most, 2 * 105 calls will be made to add, deleteOne, and hasFrequency in total.

二、题解

class FrequencyTracker {
public:unordered_map<int,int> map;unordered_map<int,int> freq;FrequencyTracker() {}void add(int number) {freq[map[number]]--;map[number]++;freq[map[number]]++;}void deleteOne(int number) {if(map[number] >= 1){freq[map[number]]--;map[number]--;freq[map[number]]++;}}bool hasFrequency(int frequency) {return freq[frequency] >= 1;}
};/*** Your FrequencyTracker object will be instantiated and called as such:* FrequencyTracker* obj = new FrequencyTracker();* obj->add(number);* obj->deleteOne(number);* bool param_3 = obj->hasFrequency(frequency);*/