Find N th Largest Element in Array

Priority Queue orders elements according to their natural order, or as per Comparator if provided at queue creation time. The default Priority Queue is implemented using Min-Heap, that is, the top element of the heap will be the minimum one in the heap. A Priority Queue does not allow null elements. it relies on the natural ordering of elements hence also does not allow non-comparable objects.

package org.wesome.dsalgo;

import java.util.PriorityQueue;

public class NthLargest {
    public static int findNthLargest(int[] list, int nThElement) {
        if (1 > nThElement) {
            System.out.println("minimum nTh element should be 1, provided " + nThElement);
            return -1;
        }
        if (list.length < nThElement) {
            System.out.println("list is empty or elements are less then " + nThElement);
            return -1;
        }
        /*  insert all the elements in PriorityQueue up to nth index */
        PriorityQueue<Integer> pq = new PriorityQueue<>();
        for (int i = 0; i < nThElement; i++) {
            pq.add(list[i]);
        }
        /*  loop from nth position to end of array   */
        for (int i = nThElement; i < list.length; i++) {
            /*  check top of PriorityQueue, if it's more than current element of array then pop the top and insert the current element  */
            if (list[i] > pq.peek()) {
                pq.poll();
                pq.add(list[i]);
            }
        }
        return pq.peek();
    }
}

package org.wesome.dsalgo;

import org.junit.jupiter.api.Assertions;
import org.junit.jupiter.api.Test;

import static org.wesome.dsalgo.NthLargest.findNthLargest;

public class FindNthLargestTest {

    @Test
    void FindNthLargestTest1() {
        int nThElement = 3;
        int[] arr = new int[]{1, 2, 3, 4, 5};
        Assertions.assertEquals(3, findNthLargest(arr, nThElement));
    }

    @Test
    void FindNthLargestTest2() {
        int nThElement = 3;
        int[] arr = new int[]{10, 9, 8, 7, 6};
        Assertions.assertEquals(8, findNthLargest(arr, nThElement));
    }

    @Test
    void FindNthLargestTest3() {
        int nThElement = 10;
        int[] arr = new int[]{8, 9, 0, 1, 2, 3};
        Assertions.assertEquals(-1, findNthLargest(arr, nThElement));
    }

    @Test
    void FindNthLargestTest4() {
        int nThElement = 0;
        int[] arr = new int[]{10, 9, 8, 7, 6};
        Assertions.assertEquals(-1, findNthLargest(arr, nThElement));
    }

    @Test
    void FindNthLargestTest5() {
        int nThElement = -1;
        int[] arr = new int[]{10, 9, 8, 7, 6};
        Assertions.assertEquals(-1, findNthLargest(arr, nThElement));
    }

    @Test
    void FindNthLargestTest6() {
        int nThElement = 5;
        int[] arr = new int[]{10, 9, 8, 7, 6};
        Assertions.assertEquals(6, findNthLargest(arr, nThElement));
    }
}

plugins {
    id 'java'
    id "io.freefair.lombok" version "6.2.0"
}

group = 'org.wesome'
version = '0.0.1-SNAPSHOT'
sourceCompatibility = JavaVersion.VERSION_1_8

configurations {
    compileOnly {
        extendsFrom annotationProcessor
    }
}

repositories {
    mavenCentral()
}

dependencies {
    testImplementation 'org.junit.jupiter:junit-jupiter:5.6.2'
}

test {
    useJUnitPlatform()
}