Sum of all prime numbers in an Array

Given an array arr[] of N positive integers. The task is to write a program to find the sum of all prime elements in the given array.

Examples:

Input: arr[] = {1, 3, 4, 5, 7}
Output: 15
There are three primes, 3, 5 and 7 whose sum =15.

Input: arr[] = {1, 2, 3, 4, 5, 6, 7}
Output: 17

Recommended: Please try your approach on {IDE} first, before moving on to the solution.

Naive Approach: A simple solution is to traverse the array and keep checking for every element if it is prime or not and add the prime element at the same time.

Efficient Approach: Generate all primes up to the maximum element of the array using the sieve of Eratosthenes and store them in a hash. Now traverse the array and find the sum of those elements which are prime using the sieve.

Below is the implementation of the efficient approach:

 `// CPP program to find sum of ` `// primes in given array. ` `#include ` `using` `namespace` `std; ` ` `  `// Function to find count of prime ` `int` `primeSum(``int` `arr[], ``int` `n) ` `{ ` `    ``// Find maximum value in the array ` `    ``int` `max_val = *max_element(arr, arr + n); ` ` `  `    ``// USE SIEVE TO FIND ALL PRIME NUMBERS LESS ` `    ``// THAN OR EQUAL TO max_val ` `    ``// Create a boolean array "prime[0..n]". A ` `    ``// value in prime[i] will finally be false ` `    ``// if i is Not a prime, else true. ` `    ``vector<``bool``> prime(max_val + 1, ``true``); ` ` `  `    ``// Remaining part of SIEVE ` `    ``prime[0] = ``false``; ` `    ``prime[1] = ``false``; ` `    ``for` `(``int` `p = 2; p * p <= max_val; p++) { ` ` `  `        ``// If prime[p] is not changed, then ` `        ``// it is a prime ` `        ``if` `(prime[p] == ``true``) { ` ` `  `            ``// Update all multiples of p ` `            ``for` `(``int` `i = p * 2; i <= max_val; i += p) ` `                ``prime[i] = ``false``; ` `        ``} ` `    ``} ` ` `  `    ``// Sum all primes in arr[] ` `    ``int` `sum = 0; ` `    ``for` `(``int` `i = 0; i < n; i++) ` `        ``if` `(prime[arr[i]]) ` `            ``sum += arr[i]; ` ` `  `    ``return` `sum; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` ` `  `    ``int` `arr[] = { 1, 2, 3, 4, 5, 6, 7 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr[0]); ` ` `  `    ``cout << primeSum(arr, n); ` ` `  `    ``return` `0; ` `} `

 `// Java program to find sum of ` `// primes in given array. ` `import` `java.util.*; ` ` `  `class` `GFG ` `{ ` ` `  `// Function to find count of prime ` `static` `int` `primeSum(``int` `arr[], ``int` `n) ` `{ ` `    ``// Find maximum value in the array ` `    ``int` `max_val = Arrays.stream(arr).max().getAsInt(); ` ` `  `    ``// USE SIEVE TO FIND ALL PRIME NUMBERS LESS ` `    ``// THAN OR EQUAL TO max_val ` `    ``// Create a boolean array "prime[0..n]". A ` `    ``// value in prime[i] will finally be false ` `    ``// if i is Not a prime, else true. ` `    ``Vector prime = ``new` `Vector<>(max_val + ``1``); ` `    ``for``(``int` `i = ``0``; i < max_val + ``1``; i++) ` `        ``prime.add(i,Boolean.TRUE); ` ` `  `    ``// Remaining part of SIEVE ` `    ``prime.add(``0``,Boolean.FALSE); ` `    ``prime.add(``1``,Boolean.FALSE); ` `    ``for` `(``int` `p = ``2``; p * p <= max_val; p++)  ` `    ``{ ` ` `  `        ``// If prime[p] is not changed, then ` `        ``// it is a prime ` `        ``if` `(prime.get(p) == ``true``)  ` `        ``{ ` ` `  `            ``// Update all multiples of p ` `            ``for` `(``int` `i = p * ``2``; i <= max_val; i += p) ` `                ``prime.add(i,Boolean.FALSE); ` `        ``} ` `    ``} ` ` `  `    ``// Sum all primes in arr[] ` `    ``int` `sum = ``0``; ` `    ``for` `(``int` `i = ``0``; i < n; i++) ` `        ``if` `(prime.get(arr[i])) ` `            ``sum += arr[i]; ` ` `  `    ``return` `sum; ` `} ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args)  ` `{ ` `    ``int` `arr[] = { ``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7` `}; ` `    ``int` `n = arr.length; ` `    ``System.out.print(primeSum(arr, n)); ` `} ` `} ` ` `  `/* This code contributed by PrinciRaj1992 */`

 `# Python3 program to find sum of ` `# primes in given array. ` ` `  `# Function to find count of prime ` `def` `primeSum( arr, n): ` `    ``# Find maximum value in the array ` `    ``max_val ``=` `max``(arr) ` ` `  `    ``# USE SIEVE TO FIND ALL PRIME NUMBERS LESS ` `    ``# THAN OR EQUAL TO max_val ` `    ``# Create a boolean array "prime[0..n]". A ` `    ``# value in prime[i] will finally be False ` `    ``# if i is Not a prime, else true. ` `    ``prime``=``[``True` `for` `i ``in` `range``(max_val ``+` `1``)] ` ` `  `    ``# Remaining part of SIEVE ` `    ``prime[``0``] ``=` `False` `    ``prime[``1``] ``=` `False` `    ``for` `p ``in` `range``(``2``, max_val ``+` `1``): ` `        ``if``(p ``*` `p > max_val): ` `            ``break` ` `  `        ``# If prime[p] is not changed, then ` `        ``# it is a prime ` `        ``if` `(prime[p] ``=``=` `True``): ` ` `  `            ``# Update all multiples of p ` `            ``for` `i ``in` `range``(p ``*` `2``, max_val``+``1``, p): ` `                ``prime[i] ``=` `False` ` `  `    ``# Sum all primes in arr[] ` `    ``sum` `=` `0` ` `  `    ``for` `i ``in` `range``(n): ` `        ``if` `(prime[arr[i]]): ` `            ``sum` `+``=` `arr[i] ` ` `  `    ``return` `sum` ` `  `# Driver code ` `arr ``=``[``1``, ``2``, ``3``, ``4``, ``5``, ``6``, ``7``] ` ` `  `n ``=` `len``(arr) ` ` `  `print``(primeSum(arr, n)) ` ` `  `# This code is contributed by mohit kumar 29 `

 `// C# program to find sum of ` `// primes in given array. ` `using` `System; ` `using` `System.Linq; ` `using` `System.Collections.Generic;  ` ` `  `class` `GFG ` `{ ` ` `  `// Function to find count of prime ` `static` `int` `primeSum(``int` `[]arr, ``int` `n) ` `{ ` `    ``// Find maximum value in the array ` `    ``int` `max_val = arr.Max(); ` ` `  `    ``// USE SIEVE TO FIND ALL PRIME NUMBERS LESS ` `    ``// THAN OR EQUAL TO max_val ` `    ``// Create a boolean array "prime[0..n]". A ` `    ``// value in prime[i] will finally be false ` `    ``// if i is Not a prime, else true. ` `    ``List<``bool``> prime = ``new` `List<``bool``>(max_val + 1); ` `    ``for``(``int` `i = 0; i < max_val + 1; i++) ` `        ``prime.Insert(i,``true``); ` ` `  `    ``// Remaining part of SIEVE ` `    ``prime.Insert(0, ``false``); ` `    ``prime.Insert(1, ``false``); ` `    ``for` `(``int` `p = 2; p * p <= max_val; p++)  ` `    ``{ ` ` `  `        ``// If prime[p] is not changed, then ` `        ``// it is a prime ` `        ``if` `(prime[p] == ``true``)  ` `        ``{ ` ` `  `            ``// Update all multiples of p ` `            ``for` `(``int` `i = p * 2; i <= max_val; i += p) ` `                ``prime.Insert(i,``false``); ` `        ``} ` `    ``} ` ` `  `    ``// Sum all primes in arr[] ` `    ``int` `sum = 0; ` `    ``for` `(``int` `i = 0; i < n; i++) ` `        ``if` `(prime[arr[i]]) ` `            ``sum += arr[i]; ` ` `  `    ``return` `sum; ` `} ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args)  ` `{ ` `    ``int` `[]arr = { 1, 2, 3, 4, 5, 6, 7 }; ` `    ``int` `n = arr.Length; ` `    ``Console.WriteLine(primeSum(arr, n)); ` `} ` `} ` ` `  `// This code contributed by Rajput-Ji `

Output:
```17
```

Time complexity : O(n*loglogn)

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