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# Divide array into two sub-arrays such that their averages are equal

• Difficulty Level : Easy
• Last Updated : 07 Jul, 2022

Given an integer array, the task is to divide an integer array into two sub-arrays to make their averages equal if possible.

Examples :

```Input : arr[] = {1, 5, 7, 2, 0};
Output : (0  1) and (2  4)
Subarrays arr[0..1] and arr[2..4] have
same average.

Input : arr[] = {4, 3, 5, 9, 11};
Output : Not possible```

A Naive Approach is to run two loops and find subarrays whose averages are equal.

Implementation:

## C++

 `// Simple C++ program to find subarrays` `// whose averages are equal` `#include` `using` `namespace` `std;`   `// Finding two subarrays` `// with equal average.` `void` `findSubarrays(``int` `arr[], ``int` `n)` `{` `    ``bool` `found = ``false``;` `    ``int` `lsum = 0;` `    ``for` `(``int` `i = 0; i < n - 1; i++)` `    ``{` `        ``lsum += arr[i];` `        ``int` `rsum = 0;` `        ``for` `(``int` `j = i + 1; j < n; j++)` `            ``rsum += arr[j];`   `        ``// If averages of arr[0...i] and ` `        ``// arr[i+1..n-1] are same. To avoid` `        ``// floating point problems we compare ` `        ``// "lsum*(n-i+1)" and "rsum*(i+1)" ` `        ``// instead of "lsum/(i+1)" and ` `        ``// "rsum/(n-i+1)"` `        ``if` `(lsum * (n - i - 1) == ` `               ``rsum * (i + 1))` `        ``{` `            ``printf``(``"From (%d %d) to (%d %d)\n"``,` `                           ``0, i, i + 1, n - 1);` `            ``found = ``true``;` `        ``}` `    ``}`   `    ``// If no subarrays found` `    ``if` `(found == ``false``)` `        ``cout << ``"Subarrays not found"` `             ``<< endl;` `}`   `// Driver code` `int` `main()` `{` `    ``int` `arr[] = {1, 5, 7, 2, 0};` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``findSubarrays(arr, n);` `    ``return` `0;` `}`

## Java

 `// Simple Java program to find subarrays` `// whose averages are equal`   `public` `class` `GFG {` `    `  `    ``// Finding two subarrays` `    ``// with equal average.` `    ``static` `void` `findSubarrays(``int``[] arr, ``int` `n)` `    ``{` `        ``boolean` `found = ``false``;` `        ``int` `lsum = ``0``;` `        `  `        ``for` `(``int` `i = ``0``; i < n - ``1``; i++)` `        ``{` `            ``lsum += arr[i];` `            ``int` `rsum = ``0``;` `            `  `            ``for` `(``int` `j = i + ``1``; j < n; j++)` `                ``rsum += arr[j];` `    `  `            ``// If averages of arr[0...i] and ` `            ``// arr[i+1..n-1] are same. To avoid` `            ``// floating point problems we compare ` `            ``// "lsum*(n-i+1)" and "rsum*(i+1)" ` `            ``// instead of "lsum/(i+1)" and ` `            ``// "rsum/(n-i+1)"` `            ``if` `(lsum * (n - i - ``1``) == ` `                                ``rsum * (i + ``1``))` `            ``{` `                ``System.out.println(``"From (0 "` `+ i ` `                        ``+ ``") to ("` `+(i + ``1``) + ``" "` `                                ``+ (n - ``1``)+ ``")"``);` `                            `  `                ``found = ``true``;` `            ``}` `        ``}` `    `  `        ``// If no subarrays found` `        ``if` `(found == ``false``)` `            ``System.out.println( ``"Subarrays not "` `                                    ``+ ``"found"``);` `    ``}` `    `  `    ``// Driver code` `    ``static` `public` `void` `main (String[] args)` `    ``{` `        ``int``[] arr = {``1``, ``5``, ``7``, ``2``, ``0``};` `        ``int` `n = arr.length;` `        ``findSubarrays(arr, n);` `    ``}` `}`   `// This code is contributed by Mukul Singh.`

## Python 3

 `# Simple Python 3 program to find subarrays` `# whose averages are equal`   `# Finding two subarrays with equal average.` `def` `findSubarrays(arr, n):`   `    ``found ``=` `False` `    ``lsum ``=` `0` `    ``for` `i ``in` `range``(n ``-` `1``):` `    `  `        ``lsum ``+``=` `arr[i]` `        ``rsum ``=` `0` `        ``for` `j ``in` `range``(i ``+` `1``, n):` `            ``rsum ``+``=` `arr[j]`   `        ``# If averages of arr[0...i] and ` `        ``# arr[i+1..n-1] are same. To avoid` `        ``# floating point problems we compare ` `        ``# "lsum*(n-i+1)" and "rsum*(i+1)" ` `        ``# instead of "lsum/(i+1)" and ` `        ``# "rsum/(n-i+1)"` `        ``if` `(lsum ``*` `(n ``-` `i ``-` `1``) ``=``=` `rsum ``*` `(i ``+` `1``)):` `            ``print``(``"From"``, ``"("``, ``0``, i, ``")"``,` `                  ``"to"``, ``"("``, i ``+` `1``, n ``-` `1``, ``")"``)` `            ``found ``=` `True`   `    ``# If no subarrays found` `    ``if` `(found ``=``=` `False``):` `        ``print``(``"Subarrays not found"``)`   `# Driver code` `if` `__name__ ``=``=` `"__main__"``:` `    `  `    ``arr ``=` `[``1``, ``5``, ``7``, ``2``, ``0``]` `    ``n ``=` `len``(arr)` `    ``findSubarrays(arr, n)`   `# This code is contributed by ita_c`

## C#

 `// Simple C# program to find subarrays` `// whose averages are equal` `using` `System;`   `public` `class` `GFG {` `    `  `    ``// Finding two subarrays` `    ``// with equal average.` `    ``static` `void` `findSubarrays(``int` `[]arr, ``int` `n)` `    ``{` `        ``bool` `found = ``false``;` `        ``int` `lsum = 0;` `        `  `        ``for` `(``int` `i = 0; i < n - 1; i++)` `        ``{` `            ``lsum += arr[i];` `            ``int` `rsum = 0;` `            `  `            ``for` `(``int` `j = i + 1; j < n; j++)` `                ``rsum += arr[j];` `    `  `            ``// If averages of arr[0...i] and ` `            ``// arr[i+1..n-1] are same. To avoid` `            ``// floating point problems we compare ` `            ``// "lsum*(n-i+1)" and "rsum*(i+1)" ` `            ``// instead of "lsum/(i+1)" and ` `            ``// "rsum/(n-i+1)"` `            ``if` `(lsum * (n - i - 1) == ` `                                  ``rsum * (i + 1))` `            ``{` `                ``Console.WriteLine(``"From ( 0 "` `+ i ` `                        ``+ ``") to("` `+ (i + 1) + ``" "` `                                ``+ (n - 1) + ``")"``);` `                            `  `                ``found = ``true``;` `            ``}` `        ``}` `    `  `        ``// If no subarrays found` `        ``if` `(found == ``false``)` `            ``Console.WriteLine( ``"Subarrays not "` `                                    ``+ ``"found"``);` `    ``}` `    `  `    ``// Driver code` `    ``static` `public` `void` `Main ()` `    ``{` `        ``int` `[]arr = {1, 5, 7, 2, 0};` `        ``int` `n = arr.Length;` `        ``findSubarrays(arr, n);` `    ``}` `}`   `// This code is contributed by anuj_67.`

## PHP

 ``

## Javascript

 ``

Output

`From (0 1) to (2 4)`

Time complexity : O(n2
Auxiliary Space : O(1)

An Efficient solution is to find sum of array elements. Initialize leftsum as zero. Run a loop and find leftsum by adding elements of array. For rightsum, we subtract leftsum from total sum then we find rightsum and find average of leftsum and rightsum as according to their index.

```1) Compute sum of all array elements. Let this
sum be "sum"
2) Initialize leftsum = 0.
3) Run a loop for i=0 to n-1.
a) leftsum  = leftsum + arr[i]
b) rightsum = sum - leftsum
c) If average of left and right are same,
print current index as output.```

Below is the implementation for above approach:

## C++

 `// Efficient C++ program for ` `// dividing array to make ` `// average equal` `#include` `using` `namespace` `std;`   `void` `findSubarrays(``int` `arr[], ``int` `n)` `{` `    ``// Find array sum` `    ``int` `sum = 0;` `    ``for` `(``int` `i = 0; i < n; i++)` `        ``sum += arr[i];`   `    ``bool` `found = ``false``;` `    ``int` `lsum = 0;` `    ``for` `(``int` `i = 0; i < n - 1; i++)` `    ``{` `        ``lsum += arr[i];` `        ``int` `rsum = sum - lsum;`   `        ``// If averages of arr[0...i] ` `        ``// and arr[i+1..n-1] are same. ` `        ``// To avoid floating point problems` `        ``// we compare "lsum*(n-i+1)" ` `        ``// and "rsum*(i+1)" instead of ` `        ``// "lsum/(i+1)" and "rsum/(n-i+1)"` `        ``if` `(lsum * (n - i - 1) == rsum * (i + 1))` `        ``{` `            ``printf``(``"From (%d %d) to (%d %d)\n"``,` `                               ``0, i, i+1, n-1);` `            ``found = ``true``;` `        ``}` `    ``}`   `    ``// If no subarrays found` `    ``if` `(found == ``false``)` `        ``cout << ``"Subarrays not found"` `             ``<< endl;` `}`   `// Driver code` `int` `main()` `{` `    ``int` `arr[] = {1, 5, 7, 2, 0};` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr);` `    ``findSubarrays(arr, n);` `    ``return` `0;` `}`

## Java

 `// Efficient Java program for ` `// dividing array to make ` `// average equal` `import` `java.util.*;` `    `  `class` `GFG` `{` `static` `void` `findSubarrays(``int` `arr[], ``int` `n)` `{` `    ``// Find array sum` `    ``int` `sum = ``0``;` `    ``for` `(``int` `i = ``0``; i < n; i++)` `        ``sum += arr[i];`   `    ``boolean` `found = ``false``;` `    ``int` `lsum = ``0``;` `    ``for` `(``int` `i = ``0``; i < n - ``1``; i++)` `    ``{` `        ``lsum += arr[i];` `        ``int` `rsum = sum - lsum;`   `        ``// If averages of arr[0...i] ` `        ``// and arr[i+1..n-1] are same. ` `        ``// To avoid floating point problems` `        ``// we compare "lsum*(n-i+1)" ` `        ``// and "rsum*(i+1)" instead of ` `        ``// "lsum/(i+1)" and "rsum/(n-i+1)"` `        ``if` `(lsum * (n - i - ``1``) == rsum * (i + ``1``))` `        ``{` `            ``System.out.printf(``"From (%d %d) to (%d %d)\n"``,` `                                      ``0``, i, i + ``1``, n - ``1``);` `            ``found = ``true``;` `        ``}` `    ``}`   `    ``// If no subarrays found` `    ``if` `(found == ``false``)` `        ``System.out.println(``"Subarrays not found"``);` `}`   `// Driver code` `static` `public` `void` `main ( String []arg)` `{` `    ``int` `arr[] = {``1``, ``5``, ``7``, ``2``, ``0``};` `    ``int` `n = arr.length;` `    ``findSubarrays(arr, n);` `}` `}`   `// This code is contributed by Princi Singh`

## Python3

 `# Efficient Python program for ` `# dividing array to make ` `# average equal`   `def` `findSubarrays(arr, n):`   `    ``# Find array sum` `    ``sum` `=` `0``;` `    ``for` `i ``in` `range``(n):` `        ``sum` `+``=` `arr[i];`   `    ``found ``=` `False``;` `    ``lsum ``=` `0``;` `    ``for` `i ``in` `range``(n ``-` `1``):` `        ``lsum ``+``=` `arr[i];` `        ``rsum ``=` `sum` `-` `lsum;`   `        ``# If averages of arr[0...i]` `        ``# and arr[i + 1..n - 1] are same.` `        ``# To avoid floating point problems` `        ``# we compare "lsum*(n - i + 1)"` `        ``# and "rsum*(i + 1)" instead of` `        ``# "lsum / (i + 1)" and "rsum/(n - i + 1)"` `        ``if` `(lsum ``*` `(n ``-` `i ``-` `1``) ``=``=` `rsum ``*` `(i ``+` `1``)):` `            ``print``(``"From (%d %d) to (%d %d)\n"``%` `                   ``(``0``, i, i ``+` `1``, n ``-` `1``));` `            ``found ``=` `True``;` `        `  `    ``# If no subarrays found` `    ``if` `(found ``=``=` `False``):` `        ``print``(``"Subarrays not found"``);`   `# Driver code` `if` `__name__ ``=``=` `'__main__'``:` `    ``arr ``=` `[ ``1``, ``5``, ``7``, ``2``, ``0` `];` `    ``n ``=` `len``(arr);` `    ``findSubarrays(arr, n);`   `# This code is contributed by Rajput-Ji`

## C#

 `// Efficient C# program for ` `// dividing array to make ` `// average equal` `using` `System;` `    `  `class` `GFG` `{` `static` `void` `findSubarrays(``int` `[]arr, ``int` `n)` `{` `    ``// Find array sum` `    ``int` `sum = 0;` `    ``for` `(``int` `i = 0; i < n; i++)` `        ``sum += arr[i];`   `    ``bool` `found = ``false``;` `    ``int` `lsum = 0;` `    ``for` `(``int` `i = 0; i < n - 1; i++)` `    ``{` `        ``lsum += arr[i];` `        ``int` `rsum = sum - lsum;`   `        ``// If averages of arr[0...i] ` `        ``// and arr[i+1..n-1] are same. ` `        ``// To avoid floating point problems` `        ``// we compare "lsum*(n-i+1)" ` `        ``// and "rsum*(i+1)" instead of ` `        ``// "lsum/(i+1)" and "rsum/(n-i+1)"` `        ``if` `(lsum * (n - i - 1) == rsum * (i + 1))` `        ``{` `            ``Console.Write(``"From ({0} {1}) to ({2} {3})\n"``,` `                                      ``0, i, i + 1, n - 1);` `            ``found = ``true``;` `        ``}` `    ``}`   `    ``// If no subarrays found` `    ``if` `(found == ``false``)` `        ``Console.WriteLine(``"Subarrays not found"``);` `}`   `// Driver code` `static` `public` `void` `Main ( String []arg)` `{` `    ``int` `[]arr = {1, 5, 7, 2, 0};` `    ``int` `n = arr.Length;` `    ``findSubarrays(arr, n);` `}` `}` `    `  `// This code is contributed by Rajput-Ji`

## Javascript

 ``

Output

`From (0 1) to (2 4)`

Time complexity : O(n)
Auxiliary Space : O(1)

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