A+ January 2017: Rock

uil/aplus-january-2017/src/Rock.java

@@ -1,2 +1,90 @@
-package PACKAGE_NAME;public class Rock {
+import java.io.File;
+import java.io.FileNotFoundException;
+import java.util.Scanner;
+
+public class Rock
+{
+    public static final char ROCK = 'R';
+    public static final char PAPER = 'P';
+    public static final char SCISSORS = 'S';
+
+    public static void main(String[] args) throws FileNotFoundException
+    {
+        Scanner in = new Scanner(new File("rock.dat"));
+        int lines = in.nextInt();
+        in.nextLine();
+
+        for (int i = 0; i < lines; i++)
+            process(in.nextLine());
+    }
+
+    public static void process(String input)
+    {
+        int wins = 0, losses = 0, ties = 0;
+        char current = ROCK; // Always starts on Rock
+
+        for (char next : input.toCharArray()) {
+            // Get match result
+            int result = check(next, current);
+
+            // Increment win/loss/tie counnt
+            switch (result) {
+                case -1:
+                    losses++;
+                    break;
+                case 0:
+                    ties++;
+                    break;
+                case 1:
+                    wins++;
+                    current = chooseNext(next); // Opponent lost, strategy applied
+                    break;
+            }
+        }
+
+        System.out.println(String.format("Wins: %d\nLosses: %d\nTies: %d\n", wins, losses, ties));
+    }
+
+    /**
+     * @param current The current RPS choice used
+     * @return The new RPS choice used by opponent
+     */
+    public static char chooseNext(char current)
+    {
+        switch (current) {
+            case ROCK:
+                return PAPER;
+            case PAPER:
+                return SCISSORS;
+            case SCISSORS:
+                return ROCK;
+        }
+        return 0;
+    }
+
+    /**
+     * Calculate the result of a Rock, Paper, Scissors match.
+     *
+     * @param self     The move used by yourself
+     * @param opponent The move used by your opponent
+     * @return A integer representing a loss (-1), tie (0), or win (1) for yourself.
+     */
+    public static int check(char self, char opponent)
+    {
+        if (self == opponent)
+            return 0;
+
+        switch (self) {
+            // Rock beats Scissors, loses to Paper
+            case ROCK:
+                return opponent == SCISSORS ? 1 : -1;
+            // Paper beats Rock, loses to Scissors
+            case PAPER:
+                return opponent == ROCK ? 1 : -1;
+            // Scissors beats Paper, loses to Rock
+            case SCISSORS:
+                return opponent == PAPER ? 1 : -1;
+        }
+        return Integer.MAX_VALUE;
+    }
 }