Create 419. Battleships in a Board.java

Author: futurus

419. Battleships in a Board.java

@@ -0,0 +1,32 @@
+// 1 scan, O(1) memory, w/o modifying input
+// works because of condition that ships are separate
+
+public class Solution {
+    public int countBattleships(char[][] board) {
+        int nship = 0;
+        
+        for (int r = 0; r < board.length; r++) {
+            for (int c = 0; c < board[r].length; c++) {
+                if (board[r][c] == 'X') {
+                    if (r == 0 && c == 0) {
+                        nship++;
+                    } else if (r == 0) {
+                        if (board[r][c-1] == '.') {
+                            nship++;
+                        }
+                    } else if (c == 0) {
+                        if (board[r-1][c] == '.') {
+                            nship++;
+                        }
+                    } else { // (r > 0 && c > 0)
+                        if (board[r-1][c] == '.' && board[r][c-1] == '.') {
+                            nship++;
+                        }
+                    }
+                }
+            }
+        }
+        
+        return nship;
+    }
+}