`Easy` `Codewriting`  `300`

Given two strings, find the number of common characters between them.

## Example

For `s1 = "aabcc"` and `s2 = "adcaa"`, the output should be
`commonCharacterCount(s1, s2) = 3`.

Strings have `3` common characters - `2` "a"s and `1` "c".

## Input/Output

- [execution time limit] 4 seconds (go)

- [input] string s1

  A string consisting of lowercase English letters.

  Guaranteed constraints: \
  `1 ≤ s1.length < 15`.

- [input] string s2

  A string consisting of lowercase English letters.

  Guaranteed constraints: \
  `1 ≤ s2.length < 15`.

- [output] integer

## [Go] Syntax Tips

``` go
// Prints help message to the console
// Returns a string
func helloWorld(name string) string {
    fmt.Printf("This prints to the console when you Run Tests");
    return "Hello, " + name;
}
```
