3. Longest Substring Without Repeating Characters.md

3. Longest Substring Without Repeating Characters

• Difficulty: Medium.
• Related Topics: Hash Table, Two Pointers, String.
• Similar Questions: Longest Substring with At Most Two Distinct Characters.

Problem

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

/**
 * @param {string} s
 * @return {number}
 */
var lengthOfLongestSubstring = function(s) {
  var map = {};
  var len = s.length;
  var max = 0;
  var start = 0;
  for (var i = 0; i < len; i++) {
    if (map[s[i]] !== undefined) {
      start = Math.max(start, map[s[i]] + 1);
    }
    map[s[i]] = i;
    max = Math.max(max, i - start + 1);
  }
  return max;
};

Explain:

nope.

Complexity:

• Time complexity : O(n).
• Space complexity : O(n).