# 3. Longest Substring Without Repeating Characters | LeetCode

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

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

Example 2: Input: s = "bbbbb" Output: 1 Explanation: The answer is "b", with the length of 1.

Example 3: 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: Input: s = "" Output: 0

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

```
public class Solution {
public int lengthOfLongestSubstring(String s) {
int n = s.length(), ans = 0;
Map<Character, Integer> map = new HashMap<>(); // current index of character
// try to extend the range [i, j]
for (int j = 0, i = 0; j < n; j++) {
if (map.containsKey(s.charAt(j))) {
i = Math.max(map.get(s.charAt(j)), i);
}
ans = Math.max(ans, j - i + 1);
map.put(s.charAt(j), j + 1);
}
return ans;
}
}
```

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