Ticket Punch Count

A tram inspector reads a ticket as a string of symbols and wants to know how many times the punch mark ch appears. Write punch_count(s, ch) that returns the number of occurrences of the single character ch in s, using recursion rather than a loop or s.count.

Examples

Input:  s = "banana", ch = "a"
Output: 3

Input:  s = "", ch = "z"
Output: 0

Constraints

• 0 <= len(s) <= 2000; ch is exactly one character.
• Recursion depth is at most len(s), well under the limit.

Goals

• Express a count as 'this character plus the count of the rest'
• Return 0 from the empty-string base case
• Avoid loops and built-in count helpers in favour of recursion