Find longest substring without repeating characters

Question

Given a string S of length N find longest substring without repeating characters.

Example:

Input:

Answer 1

Another O(n) JavaScript solution. It does not alter strings during the looping; it just keeps track of the offset and length of the longest sub string so far:

function longest(str) {
    var hash = {}, start, end, bestStart, best;
    start = end = bestStart = best = 0;
    while (end < str.length) {
        while (hash[str[end]]) hash[str[start++]] = 0;
        hash[str[end]] = 1;
        if (++end - start > best) bestStart = start, best = end - start;
    }
    return str.substr(bestStart, best);
}
 
// I/O for snippet
document.querySelector('input').addEventListener('input', function () {
    document.querySelector('span').textContent = longest(this.value);
});

Enter word:

Longest: