From b2735b1d2e43895aab13a4ce6fcc7b4887ef8d43 Mon Sep 17 00:00:00 2001
From: Stefan Waldmann <stefan.waldmann@doubleslash.de>
Date: Sun, 16 Jan 2022 18:10:28 +0100
Subject: [PATCH] Add Java implementation

---
 55_Life/java/src/java/Life.java | 127 ++++++++++++++++++++++++++++++++
 1 file changed, 127 insertions(+)
 create mode 100644 55_Life/java/src/java/Life.java

diff --git a/55_Life/java/src/java/Life.java b/55_Life/java/src/java/Life.java
new file mode 100644
index 00000000..3b592c14
--- /dev/null
+++ b/55_Life/java/src/java/Life.java
@@ -0,0 +1,127 @@
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Scanner;
+
+record Transition(int y, int x, byte newState) { }
+
+public class Life {
+
+    private static final byte DEAD  = 0;
+    private static final byte ALIVE = 1;
+
+    private final byte[][] matrix = new byte[21][67];
+    private int generation = 0;
+    private int population = 0;
+    boolean invalid = false;
+
+    private void start() throws Exception {
+        Scanner s = new Scanner(System.in);
+        printGameHeader();
+        readPattern();
+        while (true) {
+            printPattern();
+            advanceToNextGeneration();
+            s.nextLine();
+//            Thread.sleep(1000);
+        }
+    }
+
+    private void advanceToNextGeneration() {
+        List<Transition> transitions = new ArrayList<>();
+        for (int y = 0; y < matrix.length; y++) {
+            for (int x = 0; x < matrix[y].length; x++) {
+                int neighbours = countNeighbours(y, x);
+                if (matrix[y][x] == DEAD) {
+                    if (neighbours == 3) {
+                        transitions.add(new Transition(y, x, ALIVE));
+                        population++;
+                    }
+                } else {
+                    // cell is alive
+                    if (neighbours < 2 || neighbours > 3) {
+                        transitions.add(new Transition(y, x, DEAD));
+                        population--;
+                    }
+                }
+            }
+        }
+        transitions.forEach(t -> matrix[t.y()][t.x()] = t.newState());
+        generation++;
+    }
+
+    private int countNeighbours(int y, int x) {
+        int neighbours = 0;
+        for (int row = Math.max(y - 1, 0); row <= Math.min(y + 1, matrix.length - 1); row++) {
+            for (int col = Math.max(x - 1, 0); col <= Math.min(x + 1, matrix[row].length - 1); col++) {
+                if (row == y && col == x) {
+                    continue;
+                }
+                if (matrix[row][col] == ALIVE) {
+                    neighbours++;
+                }
+            }
+        }
+        return neighbours;
+    }
+
+    private void readPattern() {
+        System.out.println("ENTER YOUR PATTERN:");
+        Scanner s = new Scanner(System.in);
+        List<String> lines = new ArrayList<>();
+        String line;
+        int maxLineLength = 0;
+        boolean reading = true;
+        while (reading) {
+            System.out.print("? ");
+            line = s.nextLine();
+            if (line.equalsIgnoreCase("done")) {
+                reading = false;
+            } else {
+                // optional support for the '.' that is needed in the BASIC version
+                lines.add(line.replace('.', ' '));
+                maxLineLength = Math.max(maxLineLength, line.length());
+            }
+        }
+        fillMatrix(lines, maxLineLength);
+    }
+
+    private void fillMatrix(List<String> lines, int maxLineLength) {
+        float xMin = 33 - maxLineLength / 2f;
+        float yMin = 11 - lines.size() / 2f;
+        System.out.println("lines=" + lines.size() + " columns=" + maxLineLength + " yMin=" + yMin + " xMin=" + xMin);
+        for (int y = 0; y < lines.size(); y++) {
+            String line = lines.get(y);
+            for (int x = 1; x <= line.length(); x++) {
+                if (line.charAt(x-1) == '*') {
+                    matrix[round(yMin + y)][round(xMin + x)] = ALIVE;
+                    population++;
+                }
+            }
+        }
+    }
+
+    private int round(float f) {
+        return (int) Math.floor(f);
+    }
+
+    private void printGameHeader() {
+        System.out.println(" ".repeat(34) + "LIFE");
+        System.out.println(" ".repeat(15) + "CREATIVE COMPUTING  MORRISTOWN, NEW JERSEY");
+        System.out.println("\n\n\n");
+    }
+
+    private void printPattern() {
+        System.out.println("GENERATION: " + generation + "          POPULATION: " + population);
+        for (int y = 0; y < matrix.length; y++) {
+            for (int x = 0; x < matrix[y].length; x++) {
+                System.out.print(matrix[y][x] == 1 ? "*" : " ");
+            }
+            System.out.println();
+        }
+    }
+
+    public static void main(String[] args) throws Exception {
+        new Life().start();
+    }
+
+}