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Length of longest subsequence having sum of digits of each element as a Composite Number
  • Last Updated : 26 Oct, 2020

Given an array arr[] consisting of non-negative integers, the task is to print the length of the longest subsequence from the given array whose sum of digits of each element is a composite numbers.

Examples:

Input: arr[] = {13, 55, 7, 3, 5, 21, 233, 144, 89}
Output: 4
Explanation:Following array elements have sum of digits equal to a composite number:

  • 13 -> 1 + 3 = 4
  • 55 -> 5 + 5 = 10
  • 233 -> 2 + 3 + 3 = 8
  • 144 -> 1 + 4 + 4 = 9

Therefore, the required longest subsequence is {13, 55, 233, 144} of length 4.

Input: arr[] = {34, 13, 11, 8, 3, 55, 23}
Output: 3
Explanation: Following array elements have sum of digits equal to a composite number:



  • 13 -> 1 + 3 = 4
  • 8 -> 8 = 8
  • 55 -> 5 + 5 = 10

Therefore, the required longest subsequence is {13, 8, 55} of length 3.

 

Approach: Follow the steps given below to solve the problem:

  • Traverse the given array.
  • For each array element, check if the sum of its digits is a prime or sum of its digits is equal to 1.
  • If sum of its digits is prime, then proceed to the next array element. Otherwise, increase the length of the required subsequence by 1.
  • Finally, after complete traversal of the array, print the length of The subsequence obtained.

Below is the implementation of the above approach:

C++

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// C++ implenetation of the
// above approach
 
#include <bits/stdc++.h>
using namespace std;
 
#define N 100005
 
// Function to generate prime numbers
// using Sieve of Eratosthenes
void SieveOfEratosthenes(bool prime[],
                         int p_size)
{
    // Set 0 and 1 as non-prime
    prime[0] = false;
    prime[1] = false;
 
    for (int p = 2; p * p <= p_size; p++) {
 
        // If p is a prime
        if (prime[p]) {
 
            // Set all multiples of p as non-prime
            for (int i = p * 2; i <= p_size; i += p)
                prime[i] = false;
        }
    }
}
 
// Function to find the digit sum
// of a given number
int digitSum(int number)
{
    // Stores the sum of digits
    int sum = 0;
    while (number > 0) {
 
        // Extract digits and
        // add to the sum
        sum += (number % 10);
        number /= 10;
    }
 
    // Return the sum
    // of the digits
    return sum;
}
 
// Function to find the longest subsequence
// with sum of digits of each element equal
// to a composite number
void longestCompositeDigitSumSubsequence(
    int arr[], int n)
{
    int count = 0;
    bool prime[N + 1];
    memset(prime, true, sizeof(prime));
 
    SieveOfEratosthenes(prime, N);
 
    for (int i = 0; i < n; i++) {
 
        // Calculate sum of digits
        // of current array element
        int res = digitSum(arr[i]);
 
        // If sum of digits
        // equal to 1
        if (res == 1) {
            continue;
        }
 
        // If sum of digits is
        // a prime
        if (!prime[res]) {
            count++;
        }
    }
    cout << count << endl;
}
 
// Driver Code
int main()
{
 
    int arr[] = { 13, 55, 7, 3, 5, 1,
                  10, 21, 233, 144, 89 };
    int n = sizeof(arr)
            / sizeof(arr[0]);
 
    // Function call
    longestCompositeDigitSumSubsequence(
        arr, n);
 
    return 0;
}

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Java

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// Java implenetation of the
// above approach
import java.util.*;
 
class GFG{
 
static int N = 100005;
 
// Function to generate prime numbers
// using Sieve of Eratosthenes
static void SieveOfEratosthenes(boolean []prime,
                                int p_size)
{
     
    // Set 0 and 1 as non-prime
    prime[0] = false;
    prime[1] = false;
 
    for(int p = 2; p * p <= p_size; p++)
    {
         
        // If p is a prime
        if (prime[p])
        {
             
            // Set all multiples of p as non-prime
            for(int i = p * 2; i <= p_size; i += p)
                prime[i] = false;
        }
    }
}
 
// Function to find the digit sum
// of a given number
static int digitSum(int number)
{
     
    // Stores the sum of digits
    int sum = 0;
    while (number > 0)
    {
         
        // Extract digits and
        // add to the sum
        sum += (number % 10);
        number /= 10;
    }
 
    // Return the sum
    // of the digits
    return sum;
}
 
// Function to find the longest subsequence
// with sum of digits of each element equal
// to a composite number
static void longestCompositeDigitSumSubsequence(int []arr,
                                                int n)
{
    int count = 0;
    boolean []prime = new boolean[N + 1];
    for(int i = 0; i <= N; i++)
        prime[i] = true;
 
    SieveOfEratosthenes(prime, N);
 
    for(int i = 0; i < n; i++)
    {
         
        // Calculate sum of digits
        // of current array element
        int res = digitSum(arr[i]);
 
        // If sum of digits
        // equal to 1
        if (res == 1)
        {
            continue;
        }
 
        // If sum of digits is
        // a prime
        if (prime[res] == false)
        {
            count++;
        }
    }
    System.out.println(count);
}
 
// Driver Code
public static void main(String[] args)
{
    int []arr = { 13, 55, 7, 3, 5, 1,
                  10, 21, 233, 144, 89 };
    int n = arr.length;
 
    // Function call
    longestCompositeDigitSumSubsequence(arr, n);
}
}
 
// This code is contributed by Stream_Cipher

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Python3

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# Python3 implenetation of the
# above approach
N = 100005
 
# Function to generate prime numbers
# using Sieve of Eratosthenes
def SieveOfEratosthenes(prime,
                        p_size):
 
    # Set 0 and 1 as non-prime
    prime[0] = False
    prime[1] = False
 
    p = 2
    while p * p <= p_size:
 
        # If p is a prime
        if (prime[p]):
 
            # Set all multiples of
            # p as non-prime
            for i in range(p * 2,
                           p_size + 1, p):
                prime[i] = False
        p += 1
 
# Function to find
# the digit sum of
# a given number
def digitSum(number):
   
    # Stores the sum
    # of digits
    sum = 0
    while (number > 0):
 
        # Extract digits and
        # add to the sum
        sum += (number % 10)
        number //= 10
   
    # Return the sum
    # of the digits
    return sum
 
# Function to find the longest subsequence
# with sum of digits of each element equal
# to a composite number
def longestCompositeDigitSumSubsequence(arr, n):
 
    count = 0
    prime = [True] * (N + 1)
    SieveOfEratosthenes(prime, N)
 
    for i in range(n):
 
        # Calculate sum of digits
        # of current array element
        res = digitSum(arr[i])
 
        # If sum of digits
        # equal to 1
        if (res == 1):
            continue
       
        # If sum of digits is
        # a prime
        if (not prime[res]):
            count += 1
      
    print (count)
 
# Driver Code
if __name__ == "__main__":
 
    arr = [13, 55, 7, 3, 5, 1,
           10, 21, 233, 144, 89]
    n = len(arr)
 
    # Function call
    longestCompositeDigitSumSubsequence(arr, n)
 
# This code is contributed by Chitranayal

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C#

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// C# implenetation of the
// above approach
using System.Collections.Generic;
using System;
 
class GFG{
 
static int N = 100005;
 
// Function to generate prime numbers
// using Sieve of Eratosthenes
static void SieveOfEratosthenes(bool []prime,
                                int p_size)
{
     
    // Set 0 and 1 as non-prime
    prime[0] = false;
    prime[1] = false;
 
    for(int p = 2; p * p <= p_size; p++)
    {
 
        // If p is a prime
        if (prime[p])
        {
 
            // Set all multiples of p as non-prime
            for(int i = p * 2; i <= p_size; i += p)
                prime[i] = false;
        }
    }
}
 
// Function to find the digit sum
// of a given number
static int digitSum(int number)
{
     
    // Stores the sum of digits
    int sum = 0;
    while (number > 0)
    {
         
        // Extract digits and
        // add to the sum
        sum += (number % 10);
        number /= 10;
    }
 
    // Return the sum
    // of the digits
    return sum;
}
 
// Function to find the longest subsequence
// with sum of digits of each element equal
// to a composite number
static void longestCompositeDigitSumSubsequence(int []arr,
                                                int n)
{
    int count = 0;
    bool []prime = new bool[N + 1];
    for(int i = 0; i <= N; i++)
        prime[i] = true;
 
    SieveOfEratosthenes(prime, N);
 
    for(int i = 0; i < n; i++)
    {
         
        // Calculate sum of digits
        // of current array element
        int res = digitSum(arr[i]);
 
        // If sum of digits
        // equal to 1
        if (res == 1)
        {
            continue;
        }
 
        // If sum of digits is
        // a prime
        if (prime[res] == false)
        {
            count++;
        }
    }
    Console.WriteLine(count);
}
 
// Driver Code
public static void Main()
{
    int []arr = { 13, 55, 7, 3, 5, 1,
                  10, 21, 233, 144, 89 };
    int n = arr.Length;
 
    // Function call
    longestCompositeDigitSumSubsequence(arr, n);
}
}
 
// This code is contributed by Stream_Cipher

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Output: 

4





 

Time Complexity: O(N)
Auxiliary Space: O(log10(maxm)), where maxm is the maxm array element

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