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]