# 3.Longest Substring Without Repeating Characters <span class='tag' data-diff='medium'></span>
{%hackmd RN5D4nggQRO8wzNqxuvlNw %}

## 題目
Given a string, find the length of the longest substring without repeating characters.
**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
本來一開始想用dynamic programming解，但發現他要求的是substring而非subsequence，殺雞焉用牛刀，所以改用loop來解。首先初始化一個空的臨時字串，和max變數用來記錄目前的不重複字元字串與最大長度。接者loop過每一個字元，將臨時字串從與當前字元重複的地方切開後，把當前字元加入到臨時字串中，並更新最大substring的長度，一輪之後即可得出解答。

let temp = "",
    max = 0;

for(let c of s){
    max = Math.max(max, temp.length);
    temp = temp.slice(temp.indexOf(c) + 1);
    temp += c;
}

max = Math.max(max, temp.length);
return max;

這個方法在runtime與memory使用量上都可以贏過80%的人，潮爽der~~