10. commonCharacterCount

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".

Code

function commonCharacterCount(s1, s2) {

}