# How to find common elements between two Arrays using STL in C++?

• Difficulty Level : Medium
• Last Updated : 26 Apr, 2019

Given two arrays, find common elements between these two arrays using STL in C++.

Example:

```Input:
arr1[] = {1, 45, 54, 71, 76, 12},
arr2[] = {1, 7, 5, 4, 6, 12}
Output: {1, 12}

Input:
arr1[] = {1, 7, 5, 4, 6, 12},
arr2[] = {10, 12, 11}
Output: {1, 4, 12}
```

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

Approach: Common elements can be found with the help of set_intersection() function provided in STL.

Syntax:

```set_intersection (InputIterator1 first1, InputIterator1 last1,
InputIterator2 first2, InputIterator2 last2,
OutputIterator result);
```

 `// C++ program to find common elements ` `// between two Arrays using STL ` ` `  `#include ` `using` `namespace` `std; ` ` `  `int` `main() ` `{ ` ` `  `    ``// Get the array ` `    ``int` `arr1[] = { 1, 45, 54, 71, 76, 12 }; ` `    ``int` `arr2[] = { 1, 7, 5, 4, 6, 12 }; ` ` `  `    ``// Compute the sizes ` `    ``int` `n1 = ``sizeof``(arr1) / ``sizeof``(arr1); ` `    ``int` `n2 = ``sizeof``(arr2) / ``sizeof``(arr2); ` ` `  `    ``// Sort the arrays ` `    ``sort(arr1, arr1 + n1); ` `    ``sort(arr2, arr2 + n2); ` ` `  `    ``// Print the array ` `    ``cout << ``"First Array: "``; ` `    ``for` `(``int` `i = 0; i < n1; i++) ` `        ``cout << arr1[i] << ``" "``; ` `    ``cout << endl; ` ` `  `    ``cout << ``"Second Array: "``; ` `    ``for` `(``int` `i = 0; i < n2; i++) ` `        ``cout << arr2[i] << ``" "``; ` `    ``cout << endl; ` ` `  `    ``// Initialise a vector ` `    ``// to store the common values ` `    ``// and an iterator ` `    ``// to traverse this vector ` `    ``vector<``int``> v(n1 + n2); ` `    ``vector<``int``>::iterator it, st; ` ` `  `    ``it = set_intersection(arr1, arr1 + n1, ` `                          ``arr2, arr2 + n2, ` `                          ``v.begin()); ` ` `  `    ``cout << ``"\nCommon elements:\n"``; ` `    ``for` `(st = v.begin(); st != it; ++st) ` `        ``cout << *st << ``", "``; ` `    ``cout << ``'\n'``; ` ` `  `    ``return` `0; ` `} `

Output:

```First Array: 1 12 45 54 71 76
Second Array: 1 4 5 6 7 12

Common elements:
1, 12,
```

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