frequency-queries.js

/*
 Title: Frequency Queries
 Difficulty: Medium
 Score: 40
 Link: https://www.hackerrank.com/challenges/frequency-queries/
*/

function freqQuery(arr) {
    const result = [];
    const hash = {};
    const freq = [];

    for (let i = 0; i < arr.length; i += 1) {
        const [action, value] = arr[i];
        const initValue = hash[value] || 0;

        if (action === 1) {
            hash[value] = initValue + 1;
            freq[initValue] = (freq[initValue] || 0) - 1;
            freq[initValue + 1] = (freq[initValue + 1] || 0) + 1;
        }

        if (action === 2 && initValue > 0) {
            hash[value] = initValue - 1;
            freq[initValue - 1] += 1;
            freq[initValue] -= 1;
        }

        if (action === 3) result.push(freq[value] > 0 ? 1 : 0);
    }

    return result;
}

let input = [
    [1, 5],
    [1, 6],
    [3, 2],
    [1, 10],
    [1, 10],
    [1, 6],
    [2, 5],
    [3, 2]
    ];
console.log(freqQuery(input));