###### tags: `leetcode`, `javascript`
# 【LeetCode】Javascript - #3. Longest Substring Without Repeating Characters

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### 題目：

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

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### 大概翻譯：

給定一個字串s，求最長子字串的長度，不包含重複字元。

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例如：

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

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

Input: s = "pwwkew"
Output: 3
Explanation: The answer is "wke", with the length of 3.
Notice that the answer must be a substring, "pwke" is a subsequence and not a substring.

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var lengthOfLongestSubstring = function(s) {
    // 追蹤每個字的索引值
    const seen = new Map();
    // 追蹤當前子字串的索引值
    let start = 0;
    // 追蹤最大子字串長度
    let maxLen = 0;
    
    for(let i = 0; i < s.length; i++) {
        // 如果看到當前字元，則將開始移動到（1+此字元的最後一個索引）
        if(seen.has(s[i])) {
            start = Math.max(seen.get(s[i]) + 1, start)
        }
        seen.set(s[i], i);
        // 當前子字串長度和最大長度的最大值
        maxLen = Math.max(i - start + 1, maxLen);
    } 
    return maxLen;  
};


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*新手工程師的筆記，純粹記錄學了些啥東西
如果有前輩高人讀了我的文，文中有任何錯誤再麻煩指教指教*