LeetCode in Kotlin

1275. Find Winner on a Tic Tac Toe Game

Easy

Tic-tac-toe is played by two players A and B on a 3 x 3 grid. The rules of Tic-Tac-Toe are:

• Players take turns placing characters into empty squares ' '.
• The first player A always places 'X' characters, while the second player B always places 'O' characters.
• 'X' and 'O' characters are always placed into empty squares, never on filled ones.
• The game ends when there are three of the same (non-empty) character filling any row, column, or diagonal.
• The game also ends if all squares are non-empty.
• No more moves can be played if the game is over.

Given a 2D integer array moves where moves[i] = [rowi, coli] indicates that the ith move will be played on grid[rowi][coli]. return the winner of the game if it exists (A or B). In case the game ends in a draw return "Draw". If there are still movements to play return "Pending".

You can assume that moves is valid (i.e., it follows the rules of Tic-Tac-Toe), the grid is initially empty, and A will play first.

Example 1:

Input: moves = [[0,0],[2,0],[1,1],[2,1],[2,2]]

Output: “A”

Explanation: A wins, they always play first.

Example 2:

Input: moves = [[0,0],[1,1],[0,1],[0,2],[1,0],[2,0]]

Output: “B”

Explanation: B wins.

Example 3:

Input: moves = [[0,0],[1,1],[2,0],[1,0],[1,2],[2,1],[0,1],[0,2],[2,2]]

Output: “Draw”

Explanation: The game ends in a draw since there are no moves to make.

Constraints:

• 1 <= moves.length <= 9
• moves[i].length == 2
• 0 <= rowi, coli <= 2
• There are no repeated elements on moves.
• moves follow the rules of tic tac toe.

Solution

class Solution {
    fun tictactoe(moves: Array<IntArray>): String {
        val board = Array(3) { arrayOfNulls<String>(3) }
        for (i in moves.indices) {
            if (i % 2 == 0) {
                board[moves[i][0]][moves[i][1]] = "X"
            } else {
                board[moves[i][0]][moves[i][1]] = "O"
            }
            if (i > 3 && wins(board) != "") {
                return wins(board)
            }
        }
        return if (moves.size == 9) "Draw" else "Pending"
    }

    private fun wins(board: Array<Array<String?>>): String {
        for (i in 0..2) {
            if (board[i][0] == null) {
                continue
            }
            val str = board[i][0]
            if (str == board[i][1] && str == board[i][2]) {
                return getWinner(str)
            }
        }
        for (j in 0..2) {
            if (board[0][j] == null) {
                continue
            }
            val str = board[0][j]
            if (str == board[1][j] && str == board[2][j]) {
                return getWinner(str)
            }
        }
        if (board[1][1] == null) {
            return ""
        }
        val str = board[1][1]
        return if (str == board[0][0] && str == board[2][2] || str == board[0][2] && str == board[2][0]) {
            getWinner(str)
        } else {
            ""
        }
    }

    private fun getWinner(str: String?): String {
        return if (str == "X") {
            "A"
        } else {
            "B"
        }
    }
}

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