Chapter 7 - Maps
Exercise 1: Counting Occurrences of Strings
In the chapter 5 exercises, we asked you to count how many times the numbers 0, 1, and 2 occurred within an array. This time, your task is to count how many times letters occur within a slice.
Hint: You can set up a map with strings as its keys and integers as its values. The values can be used to keep track of the number of times each key string has occurred.