Longest Substring Without Repeating Characters

Given a string find the longest substring length of unique characters.

Example 1:

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

 Approach

Java

import java.util.ArrayList;

import java.util.List;

public class LengthOfLongestSubstring {

    public static void main(String[] args) {

        String s = "abcabcbb";

        int length = lengthOfLongestSubstring(s);

        System.out.println(length);

    }

    private static int lengthOfLongestSubstring(String s) {

        // base case

        if (s.length() == 1)

            return 1;

        // create char list

        List<Character> list = new ArrayList<>();

        int length = 0;

        // iterate till end of list

        for (int i = 0; i < s.length(); i++) {

            char c = s.charAt(i);

            // check element in list

            // not found then add

            if (!list.contains(c)) {

                list.add(c);

            } else {

                // update size

                if (list.size() > length)

                    length = list.size();

                // find remove till index

                int removeIndex = list.indexOf(c);

                // remove index

                list.remove(removeIndex);

                // remove 0 to removeindex

                for (int j = 0; j < removeIndex; j++) {

                    list.remove(0);

                }

                list.add(c);

            }

        }

        // update size

        if (list.size() > length)

            return list.size();

        return length;

    }

}

C++

#include <bits/stdc++.h>

using namespace std;

//function to find the length of 

//longest substring without

//repeating character

int lengthOfLongestSubstring(string s) 

{

      unordered_set<char> st;

      int n=s.size();

        int max1=0;

      //iterate till the length

      //of string

      for(int i=0;i<n;i++)

      {

          int len=st.size();

          st.insert(s[i]);

          //if previous len is same 

          //as new length then the new character 

          //occurs prevoius

          if(len==st.size())

            {

                //update the maximum 

                //length

               if(len>max1)

                      max1=len;

              //clear the set

              st.clear();

              //now insert into the set till we get

              //the same character as current

              //prevoiusly

              for(int j=i-1;s[j]!=s[i];j--)

                     st.insert(s[j]);

              //insert the current element

              st.insert(s[i]);

            }

          else

          {

              //uodate the maximum length

              if(st.size()>max1)

                     max1=st.size();

          }

      }

        return max1;

}

int main()

{

    string str="abcabcbb";

    int length=lengthOfLongestSubstring(str);

    cout<<length<<"\n";

    return 0;

}