public static String getSmallestAndLargest(String s, int k) {
        String smallest = "";
        String largest = "";
        
        // Complete the function
        // 'smallest' must be the lexicographically smallest substring of length 'k'
        // 'largest' must be the lexicographically largest substring of length 'k'
        String[] a=new String[s.length()-(k-1)];
        largest="\0";
        a[0]=s.substring(0,k); 
        smallest=a[0];
        for(int i=0;i<s.length()-(k-1);i++)
        {
           a[i]=s.substring(i,i+k); 
           if(largest.compareTo(a[i])<0)
           {
               largest=a[i];
           }
           if(smallest.compareTo(a[i])>0)
           {
               smallest=a[i];
           }
        }
        return smallest + "\n" + largest;
    }

public static String getSmallestAndLargest(String s, int k) {
        String smallest = "";
        String largest = "";
        
        // Complete the function
        // 'smallest' must be the lexicographically smallest substring of length 'k'
        // 'largest' must be the lexicographically largest substring of length 'k'
        
        int start = 0;
        smallest = s.substring(start, k); //give a starting point of the first 3 characters
        largest = s.substring(start, k);
        while((start + k) <= s.length()){
            
            String Temp = s.substring(start, start+k);
            smallest = (smallest.compareTo(Temp) > 0) ? Temp : smallest;
            largest = (largest.compareTo(Temp) < 0) ? Temp : largest;
            start++;
        }
        
        return smallest + "\n" + largest;
    }

    public static String getSmallestAndLargest(String s, int k) {
        java.util.SortedSet<String> set = new java.util.TreeSet<String>();
        int len = s.length() - k;
        for(int i = 0; i<=len;i++){
            set.add(s.substring(i, i+k));            
        }              
        return set.first() + "\n" + set.last();
    }

public static String getSmallestAndLargest(String s, int k) {
        String smallest = "";
        String largest = "";
        
        String[] subStr = new String[s.length() - (k-1)];
        subStr[0] = s.substring(0,k);
        
        // adding all substrings to a array 
        for(int i = 1; i < subStr.length; i++) {
        	subStr[i] = s.substring(i,i + k);
        }
        
        // using bubble sort for lexicographically element order
        for(int i = 0; i < subStr.length; i++) {
        	for(int j = 0; j < subStr.length - i - 1; j++) {
        		if(subStr[j].compareTo(subStr[j + 1]) > 0) {
        			String temp = subStr[j];
        			subStr[j] = subStr[j + 1];
        			subStr[j + 1] = temp;
        		}
        	}
        }
        
        smallest = subStr[0];
        largest = subStr[subStr.length - 1];
        
        return smallest + "\n" + largest;
    }