Longest Substring Without Repeating Characters

 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.


Approach:

Create a HashSet of Characters.
Take 2 indexes i (denotes the head of chars) and j (denotes the stretch of chars).

 public int lengthOfLongestSubstring(String s) {
        
        if(s.isEmpty())
            return 0;

        Set<Character> set =new HashSet<Character>();
        int i=0,j=0;
        int max=1;
        
        while(i<s.length()&&j<s.length())
        {
            if(!set.contains(s.charAt(j)))
               {
                   max=Math.max(max,j-i+1);
                   set.add(s.charAt(j++));
                    
                }
               
               else
               {
                   set.remove(s.charAt(i++));
               }
        }
               
               return max;
    }   

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