3. Longest Substring Without Repeating Characters

Problem

https://leetcode.com/problems/longest-substring-without-repeating-characters/

Given a string, find the length of the longest substring without repeating characters.

Examples:

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. Note that the answer must be a substring, "pwke" is a subsequence and not a substring.

Solution

 start          end
   |             |
   ======c=======c······
   |<--length-->|

         start   end->
          |      | 
   ······c======c======
          |<---length--->

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
    var head, tail, result = 0, dict = {}
    for (head = tail = 0; tail < s.length; tail += 1) {
        if (dict[s[tail]] >= head) {
            if (tail-head > result) {
                result = tail - head
            }
            head = dict[s[tail]] + 1
        }
        dict[s[tail]] = tail
    }

    if (tail-head > result) {
        return tail - head
    }

    return result
};