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5694b5a May 30, 2019
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## 题目地址

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

## 题目描述

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.
``````

## 思路

（1）如果当前遍历到的字符从未出现过，那么直接扩大右边界；

（2）如果当前遍历到的字符出现过，则缩小窗口（左边索引向右移动），然后继续观察当前遍历到的字符；

（3）重复（1）（2），直到左边索引无法再移动；

（4）维护一个结果res，每次用出现过的窗口大小来更新结果res，最后返回res获取结果。

## 关键点

1. 用一个mapper记录出现过并且没有被删除的字符
2. 用一个滑动窗口记录当前index开始的最大的不重复的字符序列
3. 用res去记录目前位置最大的长度，每次滑动窗口更新就去决定是否需要更新res

## 代码

```/**
* @param {string} s
* @return {number}
*/
var lengthOfLongestSubstring = function(s) {
const mapper = {}; // 记录已经出现过的charactor
let res = 0;
let slidingWindow = [];

for (let c of s) {
if (mapper[c]) {
// 已经出现过了
// 则删除
const delIndex = slidingWindow.findIndex(_c => _c === c);

for (let i = 0 ; i < delIndex; i++) {
mapper[slidingWindow[i]] = false;
}

slidingWindow = slidingWindow.slice(delIndex + 1).concat(c);
} else {
// 新字符
if (slidingWindow.push(c) > res) {
res = slidingWindow.length;
}
}
mapper[c] = true;
}
return res;
};```
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