Puzzle – Return all the strings with the Nth longest length

Algorithm: given a list of strings, return all the strings with the nth longest length in that list for example: list – Yuri, Ron, Interview, Longest, List, Contain and nth = 1 will return just “Interview” whereas nth = 2 will return both “Longest” and “Contain”.

Though solution to “How to find the kth largest element in an unsorted array of length n in O(n)?” can be applied to string length, how to translate back to print all the strings with n length?

Solution

I have written a simple java program which is able to find “all Nth longest elements” from a list of strings. Program is as below:

package com.howtodoinjava.examples;
 
import java.util.ArrayList;
import java.util.List;
import java.util.TreeMap;
 
public class NthLogestStringAlgorithm
{
    public static void main(String[] args)
    {
        int n = 0;
        List<String> list = new ArrayList<String>();
        list.add("Yuri");
        list.add("Ron");
        list.add("Interview");
        list.add("Longest");
        list.add("List");
        list.add("Contain");
         
        System.out.println( findNthLongestElement(list, n) );
    }
 
    private static List<String> findNthLongestElement(List<String> list, int n)
    {
        if(n < 1) {
            return null; //Handle invalid case
        }
         
        TreeMap<Integer, List<String>> map = new TreeMap<>();
         
        for(String str : list)
        {
            Integer length = str.length();
            List<String> tempList = map.get(length) != null ? map.get(length) : new ArrayList<String>();
            tempList.add(str);
            map.put(length, tempList);
        }
        return map.get( map.descendingKeySet().toArray()[n-1] );
    }
}

========Output of program=======

n = 0 => null
n = 1 => [Interview]
n = 2 => [Longest, Contain]
n = 3 => [Yuri, List]
n = 4 => [Ron]

Happy Learning !!