7.
Chapter 7 Solutions
Written by Jonathan Sande
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Solution to Exercise 1
One way to count by fives to 100 iteratively is like so:
for (int i = 5; i <= 100; i += 5) {
print(i);
}
You can accomplish the same task recursively like this:
void countByFivesRecursively([int i = 5]) {
if (i > 100) return;
print(i);
countByFivesRecursively(i + 5);
}
Solution to Exercise 2
You can print the square integers up to 100 iteratively using a while loop:
Solution to Challenge 1
- A computer’s file system uses a tree-like structure of folders and files. To print every file name, you would need to backtrack after completing the files in any particular folder. So recursion would be an appropriate solution.
- There is nothing especially tree-like about calculating a factorial, so using iteration would be just fine.
- While a family tree is indeed tree-like, no backtracking is needed to follow the matrilineal line, so iteration would be sufficient.
- JSON uses a tree-like structure with nested objects and arrays. To navigate in and out of them, backtracking would be required. So recursion would be an appropriate solution here.
Solution to Challenge 2
First, you count the current rabbit, and then you recursively add any babies it has. The base case is when a rabbit has no babies, or you’ve finished iterating through them.
Solution to Challenge 3
Although you could use a map, an efficient solution would be to use a list to cache the numbers of the Fibonacci sequence that you’ve already calculated. The index is n, and the value is the number in the sequence.