# Find the final number obtained after performing the given operation

Given an array of positive distinct integers arr[], the task is to find the final number obtained by performing the following operation on the elements of the array:
Operation: Take two unequal numbers and replace the larger number with their difference until all numbers become equal.

Examples:

Input: arr[] = {5, 2, 3}
Output: 1
5 – 3 = 2, arr[] = {2, 2, 3}
3 – 2 = 1, arr[] = {2, 2, 1}
2 – 1 = 1, arr[] = {2, 1, 1}
2 – 1 = 1, arr[] = {1, 1, 1}

Input: arr[] = {3, 9, 6, 36}
Output: 3

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

Naive approach: Since final answer will always be distinct, one can just sort the array and replace the largest term with the difference of the two largest elements and repeat the process until all the numbers become equal.

Efficient approach: From Euclidean’s algorithm, it is known that gcd(a, b) = gcd(a – b, b). This can be extended to gcd(A1, A2, A3, …, An) = gcd(A1 – A2, A2, A3, …, An).
Also, let’s say that after applying the given operation, the final number obtained be K. Hence, from the extended algorithm, it can be said that gcd(A1, A2, A3, …, An) = gcd(K, K, …, n times). Since gcd(K, K, …, n times) = K, the solution of the given problem can be found
by finding the gcd of all the elements of the array.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach ` `#include ` `using` `namespace` `std; ` ` `  `// Function to return the final number ` `// obtained after performing the ` `// given operation ` `int` `finalNum(``int` `arr[], ``int` `n) ` `{ ` ` `  `    ``// Find the gcd of the array elements ` `    ``int` `result = 0; ` `    ``for` `(``int` `i = 0; i < n; i++) { ` `        ``result = __gcd(result, arr[i]); ` `    ``} ` `    ``return` `result; ` `} ` ` `  `// Driver code ` `int` `main() ` `{ ` `    ``int` `arr[] = { 3, 9, 6, 36 }; ` `    ``int` `n = ``sizeof``(arr) / ``sizeof``(arr); ` ` `  `    ``cout << finalNum(arr, n); ` ` `  `    ``return` `0; ` `} `

## Java

 `// Java implementation of the approach ` `class` `GFG ` `{ ` ` `  `// Function to return the final number ` `// obtained after performing the ` `// given operation ` `static` `int` `finalNum(``int` `arr[], ``int` `n) ` `{ ` ` `  `    ``// Find the gcd of the array elements ` `    ``int` `result = ``0``; ` `    ``for` `(``int` `i = ``0``; i < n; i++)  ` `    ``{ ` `        ``result = __gcd(result, arr[i]); ` `    ``} ` `    ``return` `result; ` `} ` ` `  `static` `int` `__gcd(``int` `a, ``int` `b)  ` `{  ` `    ``return` `b == ``0``? a:__gcd(b, a % b);      ` `}  ` ` `  `// Driver code ` `public` `static` `void` `main(String[] args) ` `{ ` `    ``int` `arr[] = { ``3``, ``9``, ``6``, ``36` `}; ` `    ``int` `n = arr.length; ` ` `  `    ``System.out.print(finalNum(arr, n)); ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

## Python3

 `# Python3 implementation of the approach ` `from` `math ``import` `gcd as __gcd ` ` `  `# Function to return the final number ` `# obtained after performing the ` `# given operation ` `def` `finalNum(arr, n): ` ` `  `    ``# Find the gcd of the array elements ` `    ``result ``=` `arr[``0``] ` `    ``for` `i ``in` `arr: ` `        ``result ``=` `__gcd(result, i) ` `    ``return` `result ` ` `  `# Driver code ` `arr ``=` `[``3``, ``9``, ``6``, ``36``] ` `n ``=` `len``(arr) ` ` `  `print``(finalNum(arr, n)) ` ` `  `# This code is contributed by Mohit Kumar `

## C#

 `// C# implementation of the approach ` `using` `System; ` ` `  `class` `GFG ` `{ ` ` `  `// Function to return the readonly number ` `// obtained after performing the ` `// given operation ` `static` `int` `finalNum(``int` `[]arr, ``int` `n) ` `{ ` ` `  `    ``// Find the gcd of the array elements ` `    ``int` `result = 0; ` `    ``for` `(``int` `i = 0; i < n; i++)  ` `    ``{ ` `        ``result = __gcd(result, arr[i]); ` `    ``} ` `    ``return` `result; ` `} ` ` `  `static` `int` `__gcd(``int` `a, ``int` `b)  ` `{  ` `    ``return` `b == 0 ? a : __gcd(b, a % b);      ` `}  ` ` `  `// Driver code ` `public` `static` `void` `Main(String[] args) ` `{ ` `    ``int` `[]arr = { 3, 9, 6, 36 }; ` `    ``int` `n = arr.Length; ` ` `  `    ``Console.Write(finalNum(arr, n)); ` `} ` `} ` ` `  `// This code is contributed by 29AjayKumar `

Output:

```3
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