Subsecuencia más larga de números pares en una array

Dada una array arr[] que contiene N enteros, la tarea es imprimir la longitud de la subsecuencia más larga de números pares en la array.

Ejemplos:  

Entrada: arr[] = {3, 4, 11, 2, 9, 21} 
Salida: 2 
Explicación: 
La subsecuencia más larga que contiene números pares es {4, 2}. 
Por lo tanto, la respuesta es 2.

Entrada: arr[] = {6, 4, 10, 13, 9, 25} 
Salida: 3 
La subsecuencia más larga que contiene números pares es {6, 4, 10}. 
Por lo tanto, la respuesta es 3.  

Enfoque: una observación que debe hacerse a partir de la array es que la subsecuencia más larga que contiene solo un número par será el recuento total de todos los números pares. Por lo tanto, se siguen los siguientes pasos para calcular la respuesta:  

• Atraviesa la array dada elemento por elemento.
• Si el elemento es un número par , aumente la longitud de la subsecuencia resultante.
• Cuando se completa el recorrido, la longitud requerida de la subsecuencia más larga que contiene solo números pares se almacena en el contador.

A continuación se muestra la implementación del enfoque anterior:  

// C++ program to find the length of the
// longest subsequence which contains
// all even numbers
 
#include <bits/stdc++.h>
using namespace std;
#define N 100000
 
// Function to find the length of the
// longest subsequence
// which contain all even numbers
int longestEvenSubsequence(int arr[], int n)
{
    // Counter to store the
    // length of the subsequence
    int answer = 0;
 
    // Iterating through the array
    for (int i = 0; i < n; i++) {
 
        // Checking if the element is
        // even or not
        if (arr[i] % 2 == 0) {
 
            // If it is even, then
            // increment the counter
            answer++;
        }
    }
 
    return answer;
}
 
// Driver code
int main()
{
    int arr[] = { 3, 4, 11, 2, 9, 21 };
    int n = sizeof(arr) / sizeof(arr[0]);
 
    cout << longestEvenSubsequence(arr, n)
         << endl;
 
    return 0;
}

// Java program to find the length of the
// longest subsequence which contains
// all even numbers
import java.util.*;
class GFG{
 
// Function to find the length of the
// longest subsequence
// which contain all even numbers
static int longestEvenSubsequence(int arr[], int n)
{
    // Counter to store the
    // length of the subsequence
    int answer = 0;
 
    // Iterating through the array
    for (int i = 0; i < n; i++)
    {
 
        // Checking if the element is
        // even or not
        if (arr[i] % 2 == 0)
        {
 
            // If it is even, then
            // increment the counter
            answer++;
        }
    }
    return answer;
}
 
// Driver code
public static void main(String args[])
{
    int []arr = { 3, 4, 11, 2, 9, 21 };
    int n = arr.length;
 
    System.out.print(longestEvenSubsequence(arr, n));
}
}
 
// This code is contributed by Akanksha_Rai

# Python3 program to find the length
# of the longest subsequence which
# contains all even numbers
 
N = 100000
 
# Function to find the length
# of the longest subsequence
# which contain all even numbers
def longestEvenSubsequence(arr, n):
 
    # Counter to store the
    # length of the subsequence
    answer = 0
     
    # Iterating through the array
    for i in range(n):
 
        # Checking if the element
        # is even or not
        if (arr[i] % 2 == 0):
 
            # If it is even, then
            # increment the counter
            answer += 1
         
    return answer
 
# Driver code
if __name__ == "__main__":
     
    arr = [ 3, 4, 11, 2, 9, 21 ]
    n = len(arr)
 
    print(longestEvenSubsequence(arr, n))
 
# This code is contributed by chitranayal

// C# program to find the length of the
// longest subsequence which contains
// all even numbers
using System;
class GFG{
 
// Function to find the length of the
// longest subsequence
// which contain all even numbers
static int longestEvenSubsequence(int []arr, int n)
{
    // Counter to store the
    // length of the subsequence
    int answer = 0;
 
    // Iterating through the array
    for (int i = 0; i < n; i++)
    {
 
        // Checking if the element is
        // even or not
        if (arr[i] % 2 == 0)
        {
 
            // If it is even, then
            // increment the counter
            answer++;
        }
    }
    return answer;
}
 
// Driver code
public static void Main()
{
    int []arr = { 3, 4, 11, 2, 9, 21 };
    int n = arr.Length;
 
    Console.WriteLine(longestEvenSubsequence(arr, n));
}
}
 
// This code is contributed by Nidhi_Biet

<script>
// Javascript program to find the length of the
// longest subsequence which contains
// all even numbers
 
let N = 100000;
 
// Function to find the length of the
// longest subsequence
// which contain all even numbers
function longestEvenSubsequence(arr, n) {
    // Counter to store the
    // length of the subsequence
    let answer = 0;
 
    // Iterating through the array
    for (let i = 0; i < n; i++) {
 
        // Checking if the element is
        // even or not
        if (arr[i] % 2 == 0) {
 
            // If it is even, then
            // increment the counter
            answer++;
        }
    }
 
    return answer;
}
 
// Driver code
let arr = [3, 4, 11, 2, 9, 21];
let n = arr.length;
 
document.write(longestEvenSubsequence(arr, n) + "<br>");
 
// This code is contributed by _saurabh_jaiswal
</script>

2

Complejidad de tiempo: O(N) , donde N es la longitud de la array. 
Espacio Auxiliar: O(1)