Longest Substring Without Repeating Characters in javascript.

substring.js

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    var max = 0;
    var str = '';
    var i = 0;
    var cache = [];
    
    while (i < s.length) {
        if (cache[s[i]]) {
            // Found a repeating character.
            if (str.length > max) {
                max = str.length;
            }

            // Not optimal: empty substring, move i back to last position, and start collecting over.
            /*str = '';
            // Move back to last non-repeating character.
            i = cache[s[i]];
            cache = [];*/
            
            // Optimal: strip everything up to the first repeating character in our substring, and continue on.
            var start = str.indexOf(s[i]);
            str = str.substring(start + 1);
        }

        if (i < s.length) {
            str += s[i];
            cache[s[i]] = i + 1;
            i++;
        }
    }
    
    if (str.length > max) {
        max = str.length;
    }
    
    return max;
};

zexample.txt

Given "abcabcbb", the answer is "abc", which the length is 3.
Given "bbbbb", the answer is "b", with the length of 1.
Given "pwwkew", the answer is "wke", with the length of 3.

Your input
"abcabcbb"

Your stdout
a
ab
abc
bca
cab
abc
cb
b

Your answer
3