feat: kata/battleship-field-validator

kata/3-kyu/battleship-field-validator/README.md

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+# [Battleship field validator](https://www.codewars.com/kata/battleship-field-validator "https://www.codewars.com/kata/52bb6539a4cf1b12d90005b7")
+
+Write a method that takes a field for well-known board game "Battleship" as an argument and returns true if it has a valid disposition of
+ships, false otherwise. Argument is guaranteed to be 10*10 two-dimension array. Elements in the array are numbers, 0 if the cell is free and
+1 if occupied by ship.
+
+**Battleship** (also Battleships or Sea Battle) is a guessing game for two players.
+Each player has a 10x10 grid containing several "ships" and objective is to destroy enemy's forces by targeting individual cells on his
+field. The ship occupies one or more cells in the grid. Size and number of ships may differ from version to version. In this kata we will
+use Soviet/Russian version of the game.
+
+![](https://i.imgur.com/IWxeRBV.png)
+
+Before the game begins, players set up the board and place the ships accordingly to the following rules:
+
+- There must be single battleship (size of 4 cells), 2 cruisers (size 3), 3 destroyers (size 2) and 4 submarines (size 1). Any additional
+  ships are not allowed, as well as missing ships.
+- Each ship must be a straight line, except for submarines, which are just single cell.  
+  ![](https://i.imgur.com/FleBpT9.png)
+- The ship cannot overlap or be in contact with any other ship, neither by edge nor by corner.  
+  ![](https://i.imgur.com/MuLvnug.png)
+
+This is all you need to solve this kata. If you're interested in more information about the game,
+visit [this link](https://en.wikipedia.org/wiki/Battleship_(game)).

kata/3-kyu/battleship-field-validator/main/BattleField.java

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+import static java.util.stream.IntStream.range;
+
+interface BattleField {
+  static boolean fieldValidator(int[][] field) {
+    return range(0, 10).flatMap(r -> range(0, 10).map(c -> size(field, r, c))).reduce(0, Integer::sum) == 1234;
+  }
+
+  private static int size(int[][] field, int row, int col) {
+    int size = 1;
+    while (col + size < 10 && field[row][col + 1] == 1 && field[row][col + size] == 1 ||
+           row + size < 10 && field[row + 1][col] == 1 && field[row + size][col] == 1) {
+      size++;
+    }
+    return isValid(field, row, col, row < 9 && field[row + 1][col] == 1, size) ? (int) Math.pow(10, size - 1.) : 0;
+  }
+
+  private static boolean isValid(int[][] field, int row, int col, boolean vertical, int size) {
+    for (int r = Math.max(row - 1, 0); r <= Math.min(vertical ? row + size : row + 1, 9); r++) {
+      for (int c = Math.max(col - 1, 0); c <= Math.min(vertical ? col + 1 : col + size, 9); c++) {
+        if (field[r][c] == 1 && !(r == row && c == col ||
+            col + size > c && r == row && c >= col ||
+            row + size > r && c == col && r >= row)) {
+          return false;
+        }
+      }
+    }
+    return field[row][col] == 1;
+  }
+}

kata/3-kyu/battleship-field-validator/test/SolutionTest.java

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+import static org.junit.jupiter.api.Assertions.assertFalse;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import org.junit.jupiter.api.Test;
+
+class SolutionTest {
+  @Test
+  void sample() {
+    assertTrue(BattleField.fieldValidator(new int[][]{
+        {1, 0, 0, 0, 0, 1, 1, 0, 0, 0},
+        {1, 0, 1, 0, 0, 0, 0, 0, 1, 0},
+        {1, 0, 1, 0, 1, 1, 1, 0, 1, 0},
+        {1, 0, 0, 0, 0, 0, 0, 0, 0, 0},
+        {0, 0, 0, 0, 0, 0, 0, 0, 1, 0},
+        {0, 0, 0, 0, 1, 1, 1, 0, 0, 0},
+        {0, 0, 0, 0, 0, 0, 0, 0, 1, 0},
+        {0, 0, 0, 1, 0, 0, 0, 0, 0, 0},
+        {0, 0, 0, 0, 0, 0, 0, 1, 0, 0},
+        {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}}));
+    assertFalse(BattleField.fieldValidator(new int[][]{
+        {1, 0, 0, 0, 0, 0, 0, 0, 0, 0},
+        {1, 0, 1, 0, 0, 0, 0, 0, 1, 0},
+        {1, 0, 1, 0, 1, 1, 1, 0, 1, 0},
+        {1, 0, 1, 0, 0, 0, 0, 0, 0, 0},
+        {0, 0, 1, 0, 0, 0, 0, 0, 1, 0},
+        {0, 0, 0, 0, 1, 1, 1, 0, 0, 0},
+        {0, 0, 0, 0, 0, 0, 0, 0, 1, 0},
+        {0, 0, 0, 1, 0, 0, 0, 0, 0, 0},
+        {0, 0, 0, 0, 0, 0, 0, 1, 0, 0},
+        {0, 0, 0, 0, 0, 0, 0, 0, 0, 0}
+    }));
+  }
+}

kata/3-kyu/index.md

@@ -1,2 +1,3 @@
+- [Battleship field validator](battleship-field-validator "52bb6539a4cf1b12d90005b7")
 - [Make a spiral](make-a-spiral "534e01fbbb17187c7e0000c6")
 - [Path Finder #3: the Alpinist](path-finder-number-3-the-alpinist "576986639772456f6f00030c")