1209-remove-all-adjacent-duplicates-in-string-ii.js

/**
 * @param {string} s
 * @param {number} k
 * @return {string}
 */
var removeDuplicates = function (s, k) {
    const stack = []; // [char, count];

    for (const c of s) {
        if (stack.length !== 0 && stack[stack.length - 1][0] === c) {
            stack[stack.length - 1][1]++;
        } else {
            stack.push([c, 1]);
        }

        if (stack[stack.length - 1][1] === k) {
            stack.pop();
        }
    }

    return stack.reduce((res, el) => (res += el[0].repeat(el[1])), '');
};