Given a binary string s and an integer k, return true if every binary code of length k is a substring of s. Otherwise, return false.

hasAllCodes.js

/**
 * @param {string} s
 * @param {number} k
 * @return {boolean}
 */
var hasAllCodes = function(s, k) {
    // Total number of binary codes of length k
    const needed = 1 << k;  // same as Math.pow(2, k)

    // Quick fail: if s is too short to contain all codes
    // There are (s.length - k + 1) substrings of length k
    if (s.length < k || (s.length - k + 1) < needed) {
        return false;
    }

    // A set to store all unique substrings of length k
    const seen = new Set();

    // Slide a window of size k across the string
    for (let i = 0; i <= s.length - k; i++) {
        const sub = s.substring(i, i + k);
        seen.add(sub);

        // Optimization: if we've already found all possible codes, stop early
        if (seen.size === needed) {
            return true;
        }
    }

    // After scanning, check if we collected all codes
    return seen.size === needed;
};