You are given a string s consisting of lowercase English letters. A substring of s is called balanced if all distinct characters in the substring appear the same number of times. Return the length of the longest balanced substring of s.

longestBalanced.js

/**
 * @param {string} s
 * @return {number}
 */
var longestBalanced = function(s) {
    const n = s.length;
    let maxLen = 0;

    // Try every possible starting index i
    for (let i = 0; i < n; i++) {

        // Frequency array for 'a' to 'z'
        const freq = Array(26).fill(0);

        // Expand the substring from i to j
        for (let j = i; j < n; j++) {
            const idx = s.charCodeAt(j) - 97; // map 'a'..'z' to 0..25
            freq[idx]++;

            // Check if substring s[i..j] is balanced
            if (isBalanced(freq)) {
                const len = j - i + 1;
                maxLen = Math.max(maxLen, len);
            }
        }
    }

    return maxLen;
};

// Helper: returns true if all non-zero frequencies are equal
function isBalanced(freq) {
    let target = 0;

    for (let count of freq) {
        if (count === 0) continue;

        if (target === 0) {
            // First non-zero frequency becomes the target
            target = count;
        } else if (count !== target) {
            // Mismatch → not balanced
            return false;
        }
    }

    return true;
}