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Grokking the Coding Interview Patterns in Go

Design Tic-Tac-Toe

Explore how to implement a TicTacToe struct in Go that supports playing on an n by n board by tracking player moves and detecting wins. Understand the rules enforcement, move validation, and how to return the game state after each turn. This lesson helps you build foundational game design skills while practicing essential tracking techniques useful in coding interviews.

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Statement

Suppose that two players are playing a tic-tac-toe game on an n×nn \times n board. They’re following specific rules to play and win the game:

  • A move is guaranteed to be valid if a mark is placed on an empty block.
  • No more moves are allowed once a winning condition is reached.
  • A player who succeeds in placing nn of their marks in a horizontal, vertical, or diagonal row wins the game.

Implement a TicTacToe struct, which will be used by two players to play the game and win fairly.

Keep in mind the following functionalities that need to be implemented:

  • NewTicTacToe(), initializes an object of TicTacToe, allowing the players to play on a board of size n×nn \times n.
  • move(row, col, player) indicates that the player with the ID, player, places their mark on the cell (row, col). The move is guaranteed to be a valid move. At each move, this function returns the player ID if the current player wins and returns 00 if no one wins.

Constraints:

  • 2≤n≤92 \leq n \leq 9

  • player should be either 1 or 2.

  • 0≤0 \leq row, col <n< n

  • Every call to move() will be with a unique row, col combination.

  • The move() function will be called at most n2n^2 times.

Examples

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Understanding the problem

Let’s take a moment to make sure you’ve correctly understood the problem. The quiz below helps us to check if you’re solving the correct problem:

Design Tic-Tac-Toe

1.

We are given the current state of a game on a 3×33 \times 3 board, showing the moves made so far, where Player 1’s moves are denoted by a cross, and Player 2’s moves are denoted by a circle.

The following moves are now made by the players:

move(0, 2, 2)
move(1, 0, 1)

What would the result be?

A.

Player 1 wins the game.

B.

Player 2 wins the game.

C.

No one wins the game.

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Figure it out!

We have a game for you to play. Rearrange the logical building blocks to develop a clearer understanding of how to solve this problem.

Note: This puzzle relates only to the function, move(). The data structures that are set up in the constructor, NewTicTacToe, have been mentioned in the first card.

Sequence - Vertical
Drag and drop the cards to rearrange them in the correct sequence.
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Try it yourself

Implement your solution in the following coding playground.

Go
usercode > tic_tac_toe.go
package main
type TicTacToe struct {
	// Write your code here
}
// Constructor will be used to initialize TicTacToe data members 
func (this *TicTacToe) NewTicTacToe(n int) {
	// Write your code here
}
// move will be used to play a move by a specific player and identify who
// wins at each move
func (this *TicTacToe) move(row int, col int, player int) int {
	// Replace this placeholder return statement with your code
	return -1
}
Design Tic-Tac-Toe