[LeetCode] 3. Longest Substring Without Repeating Characters

最长无重复字符的子串。

题意是给一个input字符串，请输出其最长的，没有重复字符的substring。这是two pointer/sliding window的基础题。例子

Example 1:

Input: "abcabcbb"
Output: 3 
Explanation: The answer is "abc", with the length of 3. 

Example 2:

Input: "bbbbb"
Output: 1
Explanation: The answer is "b", with the length of 1.

Example 3:

Input: "pwwkew"
Output: 3
Explanation: 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.

思路是用一个hashmap或者hashset，记录当前遍历到的character是否出现过，再用两个指针维护substring的上下界。

时间O(n)

空间O(n) - hashset

 1 /**
 2  * @param {string} s
 3  * @return {number}
 4  */
 5 var lengthOfLongestSubstring = function(s) {
 6     let map = {};
 7     let max = 0;
 8     let i = 0;
 9     let j = 0;
10     while (j < s.length) {
11         if (map[s[j]]) {
12             map[s[i]] = null;
13             i++;
14         } else {
15             map[s[j]] = true;
16             max = Math.max(max, j - i + 1);
17             j++;
18         }
19     }
20     return max;
21 };