Data commit

Task/Random-Latin-squares/Java/random-latin-squares.java

@@ -0,0 +1,86 @@
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.Iterator;
+import java.util.List;
+import java.util.Objects;
+
+public class RandomLatinSquares {
+    private static void printSquare(List<List<Integer>> latin) {
+        for (List<Integer> row : latin) {
+            Iterator<Integer> it = row.iterator();
+
+            System.out.print("[");
+            if (it.hasNext()) {
+                Integer col = it.next();
+                System.out.print(col);
+            }
+            while (it.hasNext()) {
+                Integer col = it.next();
+                System.out.print(", ");
+                System.out.print(col);
+            }
+            System.out.println("]");
+        }
+        System.out.println();
+    }
+
+    private static void latinSquare(int n) {
+        if (n <= 0) {
+            System.out.println("[]");
+            return;
+        }
+
+        List<List<Integer>> latin = new ArrayList<>(n);
+        for (int i = 0; i < n; ++i) {
+            List<Integer> inner = new ArrayList<>(n);
+            for (int j = 0; j < n; ++j) {
+                inner.add(j);
+            }
+            latin.add(inner);
+        }
+        // first row
+        Collections.shuffle(latin.get(0));
+
+        // middle row(s)
+        for (int i = 1; i < n - 1; ++i) {
+            boolean shuffled = false;
+            shuffling:
+            while (!shuffled) {
+                Collections.shuffle(latin.get(i));
+                for (int k = 0; k < i; ++k) {
+                    for (int j = 0; j < n; ++j) {
+                        if (Objects.equals(latin.get(k).get(j), latin.get(i).get(j))) {
+                            continue shuffling;
+                        }
+                    }
+                }
+                shuffled = true;
+            }
+        }
+
+        // last row
+        for (int j = 0; j < n; ++j) {
+            List<Boolean> used = new ArrayList<>(n);
+            for (int i = 0; i < n; ++i) {
+                used.add(false);
+            }
+            for (int i = 0; i < n - 1; ++i) {
+                used.set(latin.get(i).get(j), true);
+            }
+            for (int k = 0; k < n; ++k) {
+                if (!used.get(k)) {
+                    latin.get(n - 1).set(j, k);
+                    break;
+                }
+            }
+        }
+
+        printSquare(latin);
+    }
+
+    public static void main(String[] args) {
+        latinSquare(5);
+        latinSquare(5);
+        latinSquare(10);
+    }
+}