# Longest Substring Without Repeating Characters Problem

## Description

LeetCode Problem 3.

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

Example 1:

``````1
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Input: s = "abcabcbb"
Output: 3
Explanation: The answer is "abc", with the length of 3.
``````

Example 2:

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

Example 3:

``````1
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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.
``````

Example 4:

``````1
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Input: s = ""
Output: 0
``````

Constraints:

• 0 <= s.length <= 5 * 104
• s consists of English letters, digits, symbols and spaces.

## Sample C++ Code

This is a C++ solution using a `hash table`.

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class Solution {
public:
int lengthOfLongestSubstring(string s) {
int len = s.size();
int max_len = 0;
unordered_map<char, int> ht;

int i = 0, j = 0;
for (i = 0; i < len; i ++) {
while ((ht.find(s[j]) == ht.end()) && (j < len)) {
ht[s[j]] = 1;
j ++;
}

max_len = max(max_len, j - i);
ht.erase(s[i]);
}
return max_len;
}
};
``````