2080. Range Frequency Queries

Design a data structure to find the frequency of a given value in a given subarray.

The frequency of a value in a subarray is the number of occurrences of that value in the subarray.

Implement the RangeFreqQuery class:

• RangeFreqQuery(int[] arr) Constructs an instance of the class with the given 0-indexed integer array arr.
• int query(int left, int right, int value) Returns the frequency of value in the subarray arr[left…right].

A subarray is a contiguous sequence of elements within an array. arr[left…right] denotes the subarray that contains the elements of nums between indices left and right (inclusive).

class RangeFreqQuery {
    vector<int> _arr[10001] = {};
public:
    RangeFreqQuery(vector<int>& arr) {
        for(int i = 0; i < arr.size(); i++)
            _arr[arr[i]].push_back(i);
    }

    int query(int left, int right, int value) {
        return upper_bound(begin(_arr[value]), end(_arr[value]), right) - lower_bound(begin(_arr[value]), end(_arr[value]), left);
    }
};

/**
 * Your RangeFreqQuery object will be instantiated and called as such:
 * RangeFreqQuery* obj = new RangeFreqQuery(arr);
 * int param_1 = obj->query(left,right,value);
 */