Position X28180

Statement

Write a function @pos_a(s, k)@ that takes a string $s$ and a non-negative integer $k$ and returns the position where the $k$ -th letter a occurs within $s$ , or -1 if the string $s$ contains fewer than $k$ letters a.

Sample session

>>> pos_a('', 1)
-1
>>> pos_a('hola', 2)
-1
>>> pos_a('ara', 3)
-1
>>> pos_a('lalaland', 3)
5
>>> pos_a('almendro', 1)
0

Information

Author: InfBesos
Language: English
Translator: InfBesos
Original language: Spanish
Other languages: Catalan Spanish
Official solutions: Python
User solutions: Python