## Three Homework Problems

### May 3, 2019

The end of the school year is approaching in many places, and students are submitting their final homework assignment, so they ask questions on the internet. Here are three questions I have seen recently:

1. Write a function `adjoin-set` that given a set of integers stored in a linked list in increasing order, and an integer to be inserted in the set, adjoins the integer to the set if it is not already in the set and returns the updated set.
2. Write a function `list-index` that finds the index within a list where a given item occurs, or returns -1 if the item is not in the list.
3. Write a function `update-count` that takes a list of key/count pairs and a key and increments the count of the given key, or adds a new key/count pair with count = 1 if the key is not present in the list.

Your task is to solve the three problems posed above. When you are finished, you are welcome to read or run a suggested solution, or to post your own solution or discuss the exercise in the comments below.