String req="";
for(int i=0;i<str.length();i++)
{
  if(!req.conatins(str.charAt(i))
  {
  }
  else{
  }

}

================================

for(int i=0;i<str.length();i++)
{
  for(int j=i+1;j<str.length();j++)
  {
     String sunstring = str.substring(i,j);
  }
}
====================
n=5

i=0  5 combinat
0
0,1
0,1,2
0,1,2,3
0,1,2,3,4
============
i=1   4 combina

1
1,2
1,2

==================
n
n(n+1)/2  formula to calculate sum of n natural number

we need to check each combination of substring wheather it is unique or not
update maximum value based on situation
=============================
Sliding window 0(n)

class Solution {
    
    public static int lengthOfLongestSubstring(String s) {
        int max = 0;
        
        
        for(int i=0;i<s.length();i++){
           // apple 0,5
            for(int j=i+1;j<=s.length();j++){
                String subs=s.substring(i,j);//0,5
                boolean check=hasUniqueCharacters(subs);
                if(check==false){
                    if(subs.length()>max){
                        max=subs.length();
                    }
                }
            }
        }
        return max;
        

       // return maxLength;
    }

    private static boolean hasUniqueCharacters(String substring) {

        String req="";
        for(int i=0;i<substring.length();i++){
            if(!req.contains(substring.charAt(i)+"")){
                req=req+substring.charAt(i)+"";
            }else{
                return true;
            }
        }
        return false;
       
    }

   
}
=============================================================

import java.awt.KeyEventDispatcher;
import java.util.*;

import com.sun.accessibility.internal.resources.accessibility;
//Longest s
public class Solution {

	public static int kDistinctChars(int k, String str) {
		// Write your code here
		 //aaaaaaaa= length of longest having one unique charactr
		 //
       int max=0;
	   for(int i=0;i<str.length();i++)
	   {
		   for(int j=i+1;j<=str.length();j++){
			   String subs=str.substring(i,j);
			  int count= totaluniquechars(subs);
			  if(count<=k){
				  if(subs.length()>max){
					  max=subs.length();
				  }
			  }
		   }
	   }
	   return max;

	}
	static int totaluniquechars(String str){
		String req="";
		int count=0;
		for(int i=0;i<str.length();i++){
			if(!req.contains(str.charAt(i)+"")){
				req=req+str.charAt(i);
			}
		}
		return req.length();
	}

}
===========================================================================