# Find number from its divisors

Given an array arr[] of N integers. The integers represent all the divisors of a number X except 1 and X itself. The task is to find the number X. If no such element is possible then print -1.

Examples:

Input: arr[] = {2, 10, 5, 4}
Output: 20

Input: arr[] = {2, 10, 5}
Output: 20

Input: arr[] = {2, 15}
Output: -1

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

Approach: Sort the given N divisors and the number X will be the first number * last number in the sorted array. Cross check if the X contradicts the given statement or not by storing all the divisors of X except 1 and X in another array and if the formed array and given array are not same then print -1, else print X.

Below is the implementation of the above approach:

## C++

 `// C++ implementation of the approach  ` `#include   ` `using` `namespace` `std;  ` `   `  `// Function that returns X  ` `int` `findX(``int` `a[], ``int` `n)  ` `{  ` `    ``// Sort the given array  ` `    ``sort(a, a + n);  ` `   `  `    ``// Get the possible X  ` `    ``int` `x = a * a[n - 1];  ` `   `  `    ``// Container to store divisors  ` `    ``vector<``int``> vec;  ` `   `  `    ``// Find the divisors of a number  ` `    ``for` `(``int` `i = 2; i * i <= x; i++) {  ` `   `  `        ``// Check if divisor  ` `        ``if` `(n % i == 0) {  ` `            ``vec.push_back(i);  ` `            ``if` `((n / i) != i)  ` `                ``vec.push_back(n / i);  ` `        ``}  ` `    ``}  ` `   `  `    ``// Check if a and vec have  ` `    ``// same elements in them  ` `    ``if` `(vec.size() == n) {  ` `        ``int` `i = 0;  ` `        ``for` `(``auto` `it : vec) {  ` `            ``if` `(a[i++] != it)  ` `                ``return` `-1;  ` `        ``}  ` `    ``}  ` `   `  `    ``return` `x;  ` `}  ` `   `  `// Drivers code  ` `int` `main()  ` `{  ` `    ``int` `a[] = { 2, 5, 4, 10 };  ` `    ``int` `n = ``sizeof``(a) / ``sizeof``(a);  ` `    ``cout << findX(a, n);  ` `   `  `    ``return` `0;  ` `}  `

## Python3

 `# Python3 implementation of the approach ` `# Function that returns X ` `import` `math ` `def` `findX(``list``,``int``): ` `    ``#Sort the given array ` `    ``list``.sort() ` `     `  `    ``#Get the possible X ` `    ``x ``=` `list``[``0``]``*``list``[``int``-``1``]; ` ` `  `    ``# Container to store divisors ` `    ``vec``=``[] ` ` `  `    ``# Find the divisors of a number ` `    ``i ``=` `2` `    ``while``(i ``*` `i <``=` `x): ` `        ``#Check if divisor ` `        ``if``(n ``%` `i ``=``=` `0``): ` `            ``vec.append(i) ` `            ``if` `((``int``/``/``i) !``=` `i): ` `                ``vec.append(``int``/``/``i) ` `        ``i ``+``=``1` ` `  `    ``# Check if a and vec have ` `    ``# same elements in them ` `    ``if``(``len``(vec) ``=``=` `int``): ` `        ``j ``=` `0` `        ``for` `it ``in` `range``(``int``): ` `            ``if``(a[j] !``=` `it): ` `                ``return` `-``1` `            ``else``: ` `                ``j ``+``=``1` `    ``return` `x ` ` `  `# Drivers code ` `a ``=` `[``2``, ``5``, ``4``, ``10``] ` `n ``=` `len``(a) ` `print``(findX(a,n)) ` ` `  `# This code is contributed by souviksarkhelkgp `

Output:

```20
```

My Personal Notes arrow_drop_up Striver(underscore)79 at Codechef and codeforces D

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Improved By : souviksarkhel