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# Find the sum of the first half and second half elements of an array

Given an array arr of size N. The task is to find the sum of the first half (N/2) elements and the second half elements (N – N/2) of an array.

Examples:

```Input : arr[] = {20, 30, 60, 10, 25, 15, 40}
Output : 110, 90
Sum of first N/2 elements 20 + 30 + 60 is 110```
```Input : arr[] = {50, 35, 20, 15}
Output : 85, 35```

Approach:

1. Initialize SumFirst and SumSecond as 0.
2. Traverse the given array.
3. Now add elements in SumFirst if the current index is less than N/2 otherwise add in SumSecond.

Below is the implementation of the above approach:

## C

 `// C program to find the sum of the first half elements and` `// second half elements of the array. Function to find find` `// the sum of the first half elements and second half` `// elements of the array.` `#include `   `void` `sum_of_elements(``int` `arr[], ``int` `n)` `{` `    ``int` `sum_of_first = 0, sum_of_second = 0;`   `    ``// adding` `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// adding first half` `        ``if` `(i < n / 2) {` `            ``sum_of_first += arr[i];` `        ``}`   `        ``// adding second half` `        ``else` `{` `            ``sum_of_second += arr[i];` `        ``}` `    ``}`   `    ``// printing answer` `    ``printf``(``"Sum of first half elements is %d\n"``,` `           ``sum_of_first);` `    ``printf``(``"Sum of second half elements is %d\n"``,` `           ``sum_of_second);` `}`   `// Driver code` `int` `main()` `{`   `    ``int` `arr[] = { 20, 30, 60, 10, 25, 15, 40 };`   `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);`   `    ``// function call` `    ``sum_of_elements(arr, n);`   `    ``return` `0;` `}`

## C#

 `// C# program to count pairs` `// whose sum divisible by 'K'` `using` `System;`   `class` `GFG {` `    ``public` `static` `void` `sum_of_elements(``int``[] arr, ``int` `n)` `    ``{`   `        ``int` `sumfirst = 0, sumsecond = 0;`   `        ``for` `(``int` `i = 0; i < n; i++) {`   `            ``// Add elements in first half sum` `            ``if` `(i < n / 2) {` `                ``sumfirst += arr[i];` `            ``}`   `            ``// Add elements in the second half sum` `            ``else` `{` `                ``sumsecond += arr[i];` `            ``}` `        ``}`   `        ``Console.WriteLine(``"Sum of first half elements is "` `                          ``+ sumfirst);`   `        ``Console.WriteLine(``"Sum of second half elements is "` `                          ``+ sumsecond);` `    ``}`   `    ``// Driver code` `    ``static` `public` `void` `Main()` `    ``{` `        ``int``[] arr = { 20, 30, 60, 10, 25, 15, 40 };` `        ``int` `n = arr.Length;`   `        ``// Function call` `        ``sum_of_elements(arr, n);` `    ``}` `}`   `// This code is contributed by nidhiva`

## C++

 `// C++ program to find the sum of the first half` `// elements and second half elements of an array`   `#include ` `using` `namespace` `std;`   `// Function to find the sum of the first half` `// elements and second half elements of an array` `void` `sum_of_elements(``int` `arr[], ``int` `n) {` `  `  `    ``int` `sumfirst = 0, sumsecond = 0;`   `    ``for` `(``int` `i = 0; i < n; i++) {` `        ``// Add elements in first half sum` `        ``if` `(i < n / 2)` `            ``sumfirst += arr[i];`   `        ``// Add elements in the second half sum` `        ``else` `            ``sumsecond += arr[i];` `    ``}`   `    ``cout << ``"Sum of first half elements is "` `<< sumfirst` `         ``<< endl;`   `    ``cout << ``"Sum of second half elements is "` `<< sumsecond` `         ``<< endl;` `}`   `// Driver Code` `int` `main()` `{` `    ``int` `arr[] = { 20, 30, 60, 10, 25, 15, 40 };`   `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);`   `    ``// Function call` `    ``sum_of_elements(arr, n);`   `    ``return` `0;` `}`

## Java

 `// Java program to count pairs` `// whose sum divisible by 'K'`   `import` `java.util.*;`   `class` `GFG {`   `    ``public` `static` `void` `sum_of_elements(``int``[] arr, ``int` `n)` `    ``{` `        ``int` `sumfirst = ``0``, sumsecond = ``0``;`   `        ``for` `(``int` `i = ``0``; i < n; i++) {`   `            ``// Add elements in first half sum` `            ``if` `(i < n / ``2``) {` `                ``sumfirst += arr[i];` `            ``}`   `            ``// Add elements in the second half sum` `            ``else` `{` `                ``sumsecond += arr[i];` `            ``}` `        ``}`   `        ``System.out.println(``"Sum of first half elements is "` `                           ``+ sumfirst);`   `        ``System.out.println(``"Sum of second half elements is "` `                           ``+ sumsecond);` `    ``}`   `    ``// Driver code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``int``[] arr = { ``20``, ``30``, ``60``, ``10``, ``25``, ``15``, ``40` `};` `        ``int` `n = arr.length;`   `        ``// Function call` `        ``sum_of_elements(arr, n);` `    ``}` `}`   `// This code is contributed by Princi Singh`

## Python3

 `# Python3 program to find the sum of` `# the first half elements and` `# second half elements of an array`   `# Function to find the sum of` `# the first half elements and` `# second half elements of an array`     `def` `sum_of_elements(arr, n):`   `    ``sumfirst ``=` `0` `    ``sumsecond ``=` `0`   `    ``for` `i ``in` `range``(n):`   `        ``# Add elements in first half sum` `        ``if` `(i < n ``/``/` `2``):` `            ``sumfirst ``+``=` `arr[i]`   `        ``# Add elements in the second half sum` `        ``else``:` `            ``sumsecond ``+``=` `arr[i]`   `    ``print``(``"Sum of first half elements is"``,` `          ``sumfirst, end``=``"\n"``)` `    ``print``(``"Sum of second half elements is"``,` `          ``sumsecond, end``=``"\n"``)`     `# Driver Code` `arr ``=` `[``20``, ``30``, ``60``, ``10``, ``25``, ``15``, ``40``]`   `n ``=` `len``(arr)`   `# Function call` `sum_of_elements(arr, n)`   `# This code is contributed` `# by Akanksha Rai`

## Javascript

 ``

Output:

```Sum of first half elements is 110
Sum of second half elements is 90```

Time complexity: O(N), as we are using a loop to traverse the array.
Auxiliary Space: O(1), as we are not using any extra space.

Approach 2: Traversing half of the array length.

The idea is to traverse half the length of the array and calculate the first sum and second sum simultaneously by

1. Initializing firstSum=0 and LastSum=0 and also traversing the array starting from the 0th index to N/2.
2. Adding values of arr[i] to the firstSum.
3. Adding values of arr[i+n/2] to the secondSum.
4. An edge case occurs when the length of the array is odd. In this case, the first sum has the sum of the first N/2 elements while secondSum has the sum of the remaining elements excluding the last element (since the loop runs for n/2 times the last element is excluded) Hence we take care of this exclusively.

Below is the code for the same.

## C#

 `// c# code to find the sum of first n/2 and last n- n/2` `// elements of an array by traversing the array length/2` `// times` `using` `System;`   `public` `class` `GFG {` `    ``public` `static` `void` `Main()` `    ``{` `        ``int``[] arr = { 20, 30, 60, 10, 25, 15, 40 };` `        ``int` `n = arr.Length;`   `        ``// Function call` `        ``sum(arr, n);` `    ``}` `    ``// function definition` `    ``public` `static` `void` `sum(``int``[] arr, ``int` `n)` `    ``{` `        ``int` `firstSum = 0, secondSum = 0;` `        ``// initializing the firstSum and secondSum variables` `        ``for` `(``int` `i = 0; i < n / 2; i++) {` `            ``// adding elements of the first half to firstSum` `            ``firstSum += arr[i];` `            ``// adding elements of the second half to` `            ``// secondSum` `            ``secondSum += arr[i + n / 2];` `        ``}` `        ``// checking for the odd case length` `        ``if` `(n % 2 != 0)` `            ``secondSum += arr[n - 1];` `        ``// printing the sums` `        ``Console.WriteLine(``"Sum of first half elements is "` `                          ``+ firstSum);` `        ``Console.WriteLine(``"Sum of second half elements is "` `                          ``+ secondSum);` `    ``}` `}`

## C++

 `// c++ code to find the sum of first n/2 and last n- n/2` `// elements of an array by traversing the array length/2` `// times` `#include ` `using` `namespace` `std;`   `// Function definition` `void` `sum(``int` `arr[], ``int` `n)` `{` `    ``int` `firstSum = 0, secondSum = 0;` `    ``// initializing the firstSum and secondSum variables` `    ``for` `(``int` `i = 0; i < n / 2; i++) {` `        ``// adding elements of the first half to firstSum` `        ``firstSum += arr[i];` `        ``// adding elements of the second half to secondSum` `        ``secondSum += arr[i + n / 2];` `    ``}` `    ``// checking for the odd case length` `    ``if` `(n % 2 != 0)` `        ``secondSum += arr[n - 1];` `    ``// printing the sums` `    ``cout << ``"Sum of first half elements is "` `<< firstSum` `         ``<< endl;`   `    ``cout << ``"Sum of second half elements is "` `<< secondSum` `         ``<< endl;` `}`   `// Driver Code` `int` `main()` `{` `    ``int` `arr[] = { 20, 30, 60, 10, 25, 15, 40 };`   `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);`   `    ``// Function call` `    ``sum(arr, n);`   `    ``return` `0;` `}`

## Java

 `// Java code to find the sum of first n/2 and last n- n/2` `// elements of an array by traversing the array length/2` `// times` `import` `java.util.*;`   `public` `class` `Main {` `    ``// Function definition` `    ``static` `void` `sum(``int` `arr[], ``int` `n)` `    ``{` `        ``int` `firstSum = ``0``, secondSum = ``0``;` `        ``// initializing the firstSum and secondSum variables` `        ``for` `(``int` `i = ``0``; i < n / ``2``; i++) {` `            ``// adding elements of the first half to firstSum` `            ``firstSum += arr[i];` `            ``// adding elements of the second half to` `            ``// secondSum` `            ``secondSum += arr[i + n / ``2``];` `        ``}` `        ``// checking for the odd case length` `        ``if` `(n % ``2` `!= ``0``)` `            ``secondSum += arr[n - ``1``];` `        ``// printing the sums` `        ``System.out.println(``"Sum of first half elements is "` `                           ``+ firstSum);` `        ``System.out.println(``"Sum of second half elements is "` `                           ``+ secondSum);` `    ``}`   `    ``// Driver Code` `    ``public` `static` `void` `main(String[] args)` `    ``{` `        ``int` `arr[] = { ``20``, ``30``, ``60``, ``10``, ``25``, ``15``, ``40` `};` `        ``int` `n = arr.length;` `        ``// Function call` `        ``sum(arr, n);` `    ``}` `}`

## Python

 `# python code to find the sum of first n/2 and last n- n/2` `# elements of an array by traversing the array length/2` `# times` `# function definition`     `def` `sum``(arr, n):` `    ``first_sum, second_sum ``=` `0``, ``0` `    ``# initializing the first_sum and second_sum variables` `    ``for` `i ``in` `range``(n ``/``/` `2``):` `        ``# adding elements of the first half to first_sum` `        ``first_sum ``+``=` `arr[i]` `        ``# adding elements of the second half to second_sum` `        ``second_sum ``+``=` `arr[i ``+` `n ``/``/` `2``]` `    ``# checking for the odd case length` `    ``if` `n ``%` `2` `!``=` `0``:` `        ``second_sum ``+``=` `arr[n ``-` `1``]` `    ``# printing the sums` `    ``print``(``'Sum of first half elements is'``, first_sum)` `    ``print``(``"Sum of second half elements is"``, second_sum)`     `# Driver Code` `arr ``=` `[``20``, ``30``, ``60``, ``10``, ``25``, ``15``, ``40``]` `n ``=` `len``(arr)` `# Function call` `sum``(arr, n)`

## Javascript

 `// JavaScript code to find the sum of first n/2 and last n- n/2` `// elements of an array by traversing the array length/2` `// times`   `// Function definition` `function` `sum(arr, n) {` `    ``let firstSum = 0, secondSum = 0;` `    ``// initializing the firstSum and secondSum variables` `    ``for` `(let i = 0; i < Math.floor(n / 2); i++) {` `        ``// adding elements of the first half to firstSum` `        ``firstSum += arr[i];` `        ``// adding elements of the second half to secondSum` `        ``secondSum += arr[i + Math.floor(n / 2)];` `    ``}` `    ``// checking for the odd case length` `    ``if` `(n % 2 !== 0)` `        ``secondSum += arr[n - 1];` `    ``// printing the sums` `    ``console.log(`Sum of first half elements is \${firstSum}`);` `    ``console.log(`Sum of second half elements is \${secondSum}`);` `}`   `// Driver Code` `const arr = [20, 30, 60, 10, 25, 15, 40];`   `const n = arr.length;`   `// Function call` `sum(arr, n);`

Output:

```Sum of first half elements is 110
Sum of second half elements is 90```

Time complexity: O(N/2)
Auxiliary Space: O(1)

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