added Minimax Algorithm to the game

opponent/minimax.go

@@ -1 +1,85 @@
 package opponent
+
+import (
+	"math"
+	"tictactoe/gamecontrol"
+)
+
+type NextMove struct {
+	Row   int
+	Col   int
+	score int
+}
+
+// iterative implementation of minimax algorithm
+func Minimax(board [3][3]string, depth int, isMaximizingPlayer bool, player string) NextMove {
+	// check if the game has ended
+	if gamecontrol.PlayerHasWon(board, "X") {
+		return NextMove{score: -10 + depth}
+	} else if gamecontrol.PlayerHasWon(board, "O") {
+		return NextMove{score: 10 - depth}
+	} else if gamecontrol.BoardisFull(board) {
+		return NextMove{score: 0}
+	}
+	// check who's turn it is
+	if isMaximizingPlayer {
+		// set max score
+		bestScore := math.MinInt64
+		var bestMove NextMove
+		// iterate through all fields
+		for i := 0; i < 3; i++ {
+			for j := 0; j < 3; j++ {
+				// check if field is empty
+				if board[i][j] == " " {
+					// make a move on this field
+					board[i][j] = player
+					// continue with the other player
+					move := Minimax(board, depth+1, false, SwitchPlayer(player))
+					// reset the field again
+					board[i][j] = " "
+					// if this move was better then the move before change values
+					if move.score > bestScore {
+						bestScore = move.score
+						bestMove = NextMove{Row: i, Col: j, score: move.score}
+					}
+				}
+			}
+		}
+		// return best possible Move
+		return bestMove
+	} else {
+		// set min score
+		bestScore := math.MaxInt64
+		var bestMove NextMove
+		// iterate through all fields
+		for i := 0; i < 3; i++ {
+			for j := 0; j < 3; j++ {
+				// check if field is empty
+				if board[i][j] == " " {
+					// make a move on this field
+					board[i][j] = player
+					// continue with the other player
+					move := Minimax(board, depth+1, true, SwitchPlayer(player))
+					// reset the field again
+					board[i][j] = " "
+					// if this move was better then the move before change values
+					if move.score < bestScore {
+						bestScore = move.score
+						bestMove = NextMove{Row: i, Col: j, score: move.score}
+					}
+				}
+			}
+		}
+		// return best possible Move
+		return bestMove
+	}
+}
+
+// this function changes the player for the minimax algorthim
+func SwitchPlayer(player string) string {
+	if player == "X" {
+		return "O"
+	} else {
+		return "X"
+	}
+}