XpguHm2K

1import java.util.HashMap;
2
3public class Main {
4	public static void main(String[] args) {
5		HashMap<String, Integer> codons = codons("atatcgcata");
6		System.out.println(codons);
7	}
8
9	// Create the static method that returns a HashMap with a String as the key and an Integer as the value.
10	// The parameter nucleotides is a string that we need to find the frequency of.
11	public static HashMap<String, Integer> codons(String nucleotides) {
12		// We need to create the HashMap to store the frequencies in.
13		HashMap<String, Integer> frequency = new HashMap<>();
14
15		// Create the for loop that starts at the beginning o the nucleotides string and ends two characters before the
16		// end of it. This is so we don't get an out of bounds substring.
17		for (int index = 0; index < nucleotides.length() - 2; index++) {
18			// Create the key to search for in the frequency HashMap.
19			// Get the three characters starting from index ending at index + 3.
20
21			/*
22				*(Assume nucleotides is atatcgcata)*
23				How does this work? Well, at the start of the for loop index is 0, the beginning of the string.
24
25				So, first iteration index = 0
26				substring(0, 0 + 3) -> substring(0, 3)
27				is going to be ata
28
29				Second iteration index = 1
30				substring(1, 1 + 3) -> substring(1, 4)
31				is going to be tat (note the index now starts at 1, so the substring is offset by 1 character)
32
33				Third iteration index = 2
34				substring(2, 2 + 3) -> substring(2, 5)
35				is going to be atc (note the index now starts at 2, so the substring is offset by 2 characters)
36
37				fourth iteration index = 3
38				substring(3, 3 + 3) -> substring(3, 6)
39				is going to be tcg (note the index now starts at 3, so the substring is offset by 3 characters)
40
41				fifth iteration index = 4
42				substring(4, 4 + 3) -> substring(4, 7)
43				is going to be cgc (note the index now starts at 4, so the substring is offset by 3 characters)
44
45				... and so on. See if you can finish the for loop.
46			*/
47			String key = nucleotides.substring(index, index + 3);
48
49			// Now to record how many times it shows up. First we need to check if the key already exists in the
50			// frequency table. If it does exist (aka if it does not equal null (!= null)) then we add one to the
51			// frequency since it has already showed up.
52			if (frequency.get(key) != null) {
53				frequency.put(key, frequency.get(key) + 1);
54			} else {
55				// In this case, the key does not exist so we need to add it to the frequency HashMap,
56				// that means he need to set the key in the HashMap to 1 since it shows up at least once.
57				frequency.put(key, 1);
58			}
59		}
60
61		return frequency;
62	}
63}