week 2 challenge

fall23/Week11/.gitignore

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+/App.class

fall23/Week11/App.java

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+package fall23.Week11;
+
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Scanner;
+import java.io.File;
+
+public class App {
+
+    /**
+     * The following iterative sequence is defined for the set of positive integers:
+     *      n -> n/2 (if n is even)
+     *      n -> 3n + 1 (if n is odd)
+     * 
+     * Using the rule above and starting with 13, we generate the following sequence:
+     *      13 -> 40 -> 20 -> 10 -> 5 -> 16 -> 8 -> 4 -> 2 -> 1
+     *
+     * This sequence contains 10 terms. Although it hasn't been proven yet (see Collatz Problem),
+     * it is thought that all starting numbers finish at 1.
+     *
+     * Which starting number, under 1 million, produces the longest chain?
+     * NOTE: Once the chain starts, the terms may go above 1 million.
+     *
+     * CREDIT: Problem 14 of Project Euler
+     *
+     * @return starting number of the longest Collatz Sequence
+     */
+    private static int collatzSequence() {
+        int n = 1;
+        int maxChain = 0;
+        int correctNum = 0;
+
+        while (n < 1_000_000) {
+            int chainLength = collatz(n, 0);
+
+            if (chainLength > maxChain) {
+                maxChain = chainLength;
+                correctNum = n;
+            }
+
+            n--;
+        }
+
+        System.out.println(correctNum);
+        return correctNum;
+    }
+
+    private static int collatz(int n, int chainLength) {
+        if(n == 1) return ++chainLength; // Base case and final link.
+
+        if(n % 2 == 0) n /= 2;
+        else n = (3 * n) + 1;
+
+        ++chainLength;
+
+        return collatz(n, chainLength);
+    }
+
+    /**
+     * Background:
+     *      January 1 1900 was a Monday.
+     *      April, June, September, and November have 30 days.
+     *      January, March, May, July, August, October, and December have 31 days.
+     *      February has 28 days and on leap years 29.
+     *      A leap year occurs on any year evenly divisible by 4, but not on a century unless 
+     *          it is divisble by 400.
+     *
+     * How many Sundays fell on the first of the month during the 20th century?
+     *      (January 1 1901 to December 31 2000).
+     *
+     * CREDIT: Problem 19 of Project Euler
+     *
+     * @return the number of Sundays
+     */
+    private static int countingSundays() {
+        return 1; // TODO
+    }
+
+    /**
+     * Using names.txt, a text file containing more than five-thousand first names,
+     * begin by sorting it in alphabetical order. Then work out the alphabetical value
+     * of each name, multiply this value by its alphabetical position in the list to obtain
+     * a name score.
+     *
+     * For example, when the list is sorted into alphabetical order, COLIN, which is worth
+     *      3 + 15 + 12 + 9 + 14 = 53
+     * is the 938th name in the list. So COLIN would have a score of
+     *      938 x 53 = 49714
+     *
+     * What is the total of all the name scores in the file?
+     * 
+     * CREDIT: Problem 22 of Project Euler
+     *
+     * @return the total of the name scores.
+     */
+    private static int nameScores() {
+        ArrayList<String> names = readNames();
+        int sum = 0;
+
+        Collections.sort(names);
+
+        int counter = 1;
+        for (String name : names) {
+            int nameScore = 0;
+            char[] n = name.toCharArray();
+            for (char c : n) {
+                nameScore += (c - 64);
+            }
+
+            nameScore *= counter;
+            sum+= nameScore;
+
+            counter++;
+        }
+
+        System.out.println("sum of name scores: " + sum);
+        return sum;
+    }
+
+    private static ArrayList<String> readNames() {
+        ArrayList<String> list = new ArrayList<>();
+
+        File f = new File("names.txt");
+
+        try (Scanner scan = new Scanner(f)) {
+            String str = scan.nextLine();
+
+            String[] strings = str.split(",");
+
+            for (String s : strings)
+                list.add(s.substring(1, s.length() - 1));
+
+        } catch (Exception e) {
+            System.out.println("Error reading file.");
+        }
+
+        return list;
+    }
+
+    private static void printNames(ArrayList<String> names) {
+        for (String name : names)
+            System.out.println(name);
+    }
+
+    public static void main(String[] args) {
+        //System.out.println(collatz(13, 0));
+        if(collatzSequence() != 837799) System.out.println("Your solution is incorrect...");
+        else System.out.println("Your Collatz Sequence solution is correct!");
+
+        /*
+        if(countingSundays() != 171) System.out.println("Your solution is incorrect...");
+        else System.out.println("Your Counting Sundays solution is correct!");
+
+        if(nameScores() != 871198282) System.out.println("Your solution is incorrect...");
+        else System.out.println("Your Name Scores solution is correct!");
+        */
+    }
+}

fall23/Week11/run

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+#!/bin/zsh
+
+javac *.java
+java App
+
+rm *.class