tictactoe: hard ai sets first empy field if theres no better option

src/main/java/de/tims/tictactoe/ai/AIHard.java

@@ -19,13 +19,17 @@ public class AIHard implements TicTacToeAI {
 
 	@Override
 	public void calculateNextMove() {
+		char[][] board = gl.getBoard();
+		int row;
+		int col;
+		
 		int charsInRow = 0;
 		int charsInCol = 0;
 		int charsInDiag = 0;
-		char[][] board = gl.getBoard();
+		char actualChar;
 		
 		for (int i = 0; i < 2; i++) {
-			char actualChar = (i == 0) ? AI_CHAR : PLAYER_CHAR;
+			actualChar = (i == 0) ? AI_CHAR : PLAYER_CHAR;
 			
 			for (int j = 0; j < BOARD_SIZE; j++) {
 				charsInRow = countCharsInRow(j, actualChar);
@@ -35,8 +39,11 @@ public class AIHard implements TicTacToeAI {
 					charsInDiag = countCharsInDiag(j, actualChar);
 					if (charsInDiag == BOARD_SIZE - 1) {
 						for (int k = 0; k < BOARD_SIZE; k++) {
-							if (board[k][(j == 0) ? k : BOARD_SIZE - 1 - k] == EMPTY_CHAR) {
-								gl.setField(k, (j == 0) ? k : BOARD_SIZE - 1 -k, AI_CHAR);
+							row = k;
+							col = (j == 0) ? k : BOARD_SIZE - 1 - k;
+							
+							if (board[row][col] == EMPTY_CHAR) {
+								gl.setField(row, col, AI_CHAR);
 								return;
 							}
 						}
@@ -45,8 +52,11 @@ public class AIHard implements TicTacToeAI {
 				
 				if (charsInRow == BOARD_SIZE - 1 || charsInCol == BOARD_SIZE - 1) {
 					for (int k = 0; k < BOARD_SIZE; k++) {
-						if (board[(charsInRow == BOARD_SIZE - 1) ? j : k][(charsInRow == BOARD_SIZE - 1) ? k : j] == EMPTY_CHAR) {
-							gl.setField((charsInRow == BOARD_SIZE - 1) ? j : k, (charsInRow == BOARD_SIZE - 1) ? k : j, AI_CHAR);
+						row = (charsInRow == BOARD_SIZE - 1) ? j : k;
+						col = (charsInRow == BOARD_SIZE - 1) ? k : j;
+						
+						if (board[row][col] == EMPTY_CHAR) {
+							gl.setField(row, col, AI_CHAR);
 							return;
 						}
 					}
@@ -56,26 +66,37 @@ public class AIHard implements TicTacToeAI {
 		
 		if (board[BOARD_SIZE / 2][BOARD_SIZE / 2] == EMPTY_CHAR) {			
 			gl.setField(BOARD_SIZE / 2, BOARD_SIZE / 2, AI_CHAR);
+			return;
 		} else if (board[BOARD_SIZE / 2][BOARD_SIZE / 2] == AI_CHAR && (board[0][0] == AI_CHAR || board[0][BOARD_SIZE - 1] == AI_CHAR || board[BOARD_SIZE - 1][0] == AI_CHAR || board[BOARD_SIZE - 1][BOARD_SIZE - 1] == AI_CHAR)) {
+			int onwCharsInRow = 0;
+			int ownCharsInCol = 0;
+			int emptyCharsInRow = 0;
+			int emptyCharsInCol = 0;
+			
 			for (int i = BOARD_SIZE - 2; i > 0; i--) {				
 				for (int j = 0; j < BOARD_SIZE; j += BOARD_SIZE - 1) {
 					for (int k = 1; k < BOARD_SIZE - 1; k++) {
-						if (countCharsInRow(j, AI_CHAR) == i && countCharsInCol(k, AI_CHAR) == i && countCharsInRow(j, EMPTY_CHAR) == BOARD_SIZE -i && countCharsInCol(k, EMPTY_CHAR) == BOARD_SIZE - i) {
-							gl.setField(j, k, AI_CHAR);
-							return;
-						}
+						for (int l = 0; l < 2; l++) {
+							row = (l == 0) ? j : k;
+							col = (l == 0) ? k : j;
 							
-						if (countCharsInRow(k, AI_CHAR) == i && countCharsInCol(j, AI_CHAR) == i && countCharsInRow(k, EMPTY_CHAR) == BOARD_SIZE -i && countCharsInCol(j, EMPTY_CHAR) == BOARD_SIZE - i) {
-							gl.setField(k, j, AI_CHAR);
-							return;
+							onwCharsInRow = countCharsInRow(row, AI_CHAR);
+							ownCharsInCol = countCharsInCol(col, AI_CHAR);
+							emptyCharsInRow = countCharsInRow(row, EMPTY_CHAR);
+							emptyCharsInCol = countCharsInCol(col, EMPTY_CHAR);
+							
+							if (onwCharsInRow >= i && ownCharsInCol >= i && emptyCharsInRow >= BOARD_SIZE - onwCharsInRow && emptyCharsInCol == BOARD_SIZE - ownCharsInCol) {
+								gl.setField(row, col, AI_CHAR);
+								return;
+							}
 						}
 					}
 				}
 			}
 		} else {
 			boolean emptyEdgeFound = false;
-			int row = -1;
-			int col = -1;
+			row = -1;
+			col = -1;
 			int prioRow = -1;
 			int prioCol = -1;
 			
@@ -99,7 +120,22 @@ public class AIHard implements TicTacToeAI {
 				}
 			}
 			
-			gl.setField((prioRow != -1) ? prioRow : row, (prioCol != -1) ? prioCol : col, AI_CHAR);
+			if (row != -1 && col != -1) {
+				row = (prioRow != -1) ? prioRow : row;
+				col = (prioCol != -1) ? prioCol : col;
+				
+				gl.setField(row, col, AI_CHAR);
+				return;
+			}	
+		}
+		
+		for (row = 0; row < BOARD_SIZE; row++) {
+			for (col = 0; col < BOARD_SIZE; col++) {
+				if (board[row][col] == EMPTY_CHAR) {
+					gl.setField(row, col, AI_CHAR);
+					return;
+				}
+			}
 		}
 	}
 	

src/test/java/de/tims/tictactoe/ai/AIHardTest.java

@@ -165,6 +165,17 @@ class AIHardTest {
 		verify(gl, times(1)).setField(1, 2, realChar);
 	}
 	
+	@Test
+	void setFirstFreeFieldIfNoBetterOpportunities() {
+		char realChar = 'o';
+		doReturn(new char[][] { {'o', 'x', 'x'}, {'x', 'o', 'o'}, {'o', '-', 'x'} }).when(gl).getBoard();
+		
+		TicTacToeAI ai = new AIHard(gl);
+		ai.calculateNextMove();
+		
+		verify(gl, times(1)).setField(2, 1, realChar);
+	}
+	
 	@ParameterizedTest
 	@MethodSource("testCasesForCountCharsInRow")
 	void countCharsInRowTest(String testName, char[][] board, int rowNum, char charToCount, int expectedResult) {