How To Find A Second Largest Element in an Array?

Gaurav B Sinha

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11 Sep 2015CPOL

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Finding the second largest element in an array using Linq

Introduction

The code snippet below will show you how to find a second largest element in an array:

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace MSMUTest
{
    class Program
    {
        /*
         * Write a function that accepts an array of non-negative integers and 
         * returns the second largest integer in the array. Return -1 if there is no second largest.
         */

        public int [] AcceptArrayElements(int count)
        {
            int[] inputElement = new int[count];
            for (int cnt = 0; cnt < count; cnt++)
            {
                inputElement[cnt] = Convert.ToInt32(Console.ReadLine());
            }
            return inputElement;
        }
        

 public int FindSecondLargestElement(int[] inputElements)
        {

            var result = (from elements in inputElements
                          orderby elements descending
                          select elements).Distinct().Skip(1).Take(1);
#region ForBeginners
            // May use below code block if not much versed in linq.
            //var result = (from elements in inputElements
            //              orderby elements descending
            //              select elements
          //  int scndLargestNumber = -1;
            //int [] finalArray = result.ToArray();
            //for (int cnt = 0; cnt < finalArray.Length; cnt++)
            //{
               
            //    if ( finalArray[cnt] < finalArray[0])
            //    {
            //        scndLargestNumber = finalArray[cnt];
            //        break;
            //    }
               
            //}
#endregion

            return result.FirstOrDefault();
        }

        static void Main(string[] args)
        {
            Console.WriteLine("Please Enter Count");
            int count =Convert.ToInt32( Console.ReadLine());
            Program test = new Program();
            Console.WriteLine("Enter Your Number");
            int[] inputElements = test.AcceptArrayElements(count);
            for (int cnt = 0; cnt < inputElements.Length; cnt++)
            {
                Console.WriteLine("Your Input Element At Position {0} is {1}.", 
					cnt, inputElements[cnt]);
            }
            Console.WriteLine("Second Largest Element In Your Provided Input Is {0} ", 
				test.FindSecondLargestElement(inputElements));

        }
    }
}

License

This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By

Gaurav B Sinha

Technical Lead

India

This member has not yet provided a Biography. Assume it's interesting and varied, and probably something to do with programming.

namespace SecondLargest { class Program { static Random rnd = new Random(); static int count = 1000; public static void Main(string[] args) { int[] inputElements = new int[count]; for (int cnt = 0; cnt < count; cnt++) { inputElements[cnt] = rnd.Next(); } Stopwatch sw = new Stopwatch(); sw.Restart(); int Second = FindSecondLargestElement_Linq(inputElements); sw.Stop(); Console.WriteLine("Second largest {0}, found using O(N log N) LINQ-SQL, {1}", Second, sw.Elapsed); sw.Restart(); Second = FindSecondLargestElement_Linq2(inputElements); sw.Stop(); Console.WriteLine("Second largest {0}, found using O(N log N) LINQ, {1}", Second, sw.Elapsed); sw.Restart(); Second = FindSecondLargestElement_Imperative(inputElements); sw.Stop(); Console.WriteLine("Second largest {0}, found using O(N) imperative, {1}", Second, sw.Elapsed); Console.ReadKey(true); } public static int FindSecondLargestElement_Linq(int[] inputElements) { return (from elements in inputElements orderby elements descending select elements).Distinct().Skip(1).FirstOrDefault(); } public static int FindSecondLargestElement_Linq2(int[] inputElements) { return inputElements.OrderByDescending(k => k).Distinct().Skip(1).FirstOrDefault(); } public static int FindSecondLargestElement_Imperative(int[] inputElements) { int L = int.MinValue; int S = int.MinValue; for (int i = 0; i < inputElements.Length; i++) { int V = inputElements[i]; if (V > L) { S = L; L = V; } else if ((L > V) && (V > S)) { S = V; } } return S; } } }

Second largest 2137772579, found using O(N log N) LINQ-SQL, 00:00:00.0061404 Second largest 2137772579, found using O(N log N) LINQ, 00:00:00.0003753 Second largest 2137772579, found using O(N) imperative, 00:00:00.0001044

Second largest 2140265055, found using O(N log N) LINQ-SQL, 00:00:00.0052420 Second largest 2140265055, found using O(N log N) LINQ-SQL, 00:00:00.0001626 Second largest 2140265055, found using O(N log N) LINQ-SQL, 00:00:00.0001410 Second largest 2140265055, found using O(N log N) LINQ, 00:00:00.0003709 Second largest 2140265055, found using O(N log N) LINQ, 00:00:00.0001407 Second largest 2140265055, found using O(N log N) LINQ, 00:00:00.0001401 Second largest 2140265055, found using O(N) imperative, 00:00:00.0001035 Second largest 2140265055, found using O(N) imperative, 00:00:00.0000011 Second largest 2140265055, found using O(N) imperative, 00:00:00.0000008

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How To Find A Second Largest Element in an Array?

Introduction

License

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