Duplicate Characters in a String

Given a string 'S' of length 'N', identify and return all the characters in the string that appear more than once along with their frequency.

Example:

Input:

 N = 5
 S = 'GEEK'

Output:

[('E', 2)]

Explanation:

The character 'E' is the only one duplicated in the string with a frequency of 2.

Constraints:

• 1 <= T <= 5
• 1 <= N <= 10^5

Time Limit: 1 second