| 4 | 4 | // |
| 5 | 5 | |
| 6 | 6 | /** |
| 7 | | * @param {string[]} board |
| 8 | | * @returns {string} |
| 7 | * Determines the state of a Tic-Tac-Toe game based on the given board. |
| 8 | * |
| 9 | * @param {string[]} board - An array of 3 strings, each representing a row of the 3x3 board. |
| 10 | * Each character is either 'X', 'O', or ' ' (empty space). |
| 11 | * @returns {string} - Returns one of 'win', 'draw', or 'ongoing'. |
| 12 | * @throws {Error} - Throws an error for invalid board states with specific messages. |
| 9 | 13 | */ |
| 10 | 14 | export const gamestate = (board) => { |
| 11 | | throw new Error('Remove this line and implement the function'); |
| 15 | // Validate board structure |
| 16 | if (!Array.isArray(board) || board.length !== 3) { |
| 17 | throw new Error('Invalid board: must have 3 rows'); |
| 18 | } |
| 19 | |
| 20 | for (let i = 0; i < 3; i++) { |
| 21 | if (typeof board[i] !== 'string' || board[i].length !== 3) { |
| 22 | throw new Error('Invalid board: each row must be a string of length 3'); |
| 23 | } |
| 24 | for (let j = 0; j < 3; j++) { |
| 25 | const char = board[i][j]; |
| 26 | if (char !== 'X' && char !== 'O' && char !== ' ') { |
| 27 | throw new Error('Invalid board: contains invalid characters'); |
| 28 | } |
| 29 | } |
| 30 | } |
| 31 | |
| 32 | // Count Xs and Os |
| 33 | let countX = 0; |
| 34 | let countO = 0; |
| 35 | |
| 36 | for (let i = 0; i < 3; i++) { |
| 37 | for (let j = 0; j < 3; j++) { |
| 38 | if (board[i][j] === 'X') countX++; |
| 39 | if (board[i][j] === 'O') countO++; |
| 40 | } |
| 41 | } |
| 42 | |
| 43 | // Check for wins |
| 44 | const wins = (player) => { |
| 45 | // Check rows |
| 46 | for (let i = 0; i < 3; i++) { |
| 47 | if (board[i][0] === player && board[i][1] === player && board[i][2] === player) { |
| 48 | return true; |
| 49 | } |
| 50 | } |
| 51 | |
| 52 | // Check columns |
| 53 | for (let j = 0; j < 3; j++) { |
| 54 | if (board[0][j] === player && board[1][j] === player && board[2][j] === player) { |
| 55 | return true; |
| 56 | } |
| 57 | } |
| 58 | |
| 59 | // Check diagonals |
| 60 | if (board[0][0] === player && board[1][1] === player && board[2][2] === player) { |
| 61 | return true; |
| 62 | } |
| 63 | |
| 64 | if (board[0][2] === player && board[1][1] === player && board[2][0] === player) { |
| 65 | return true; |
| 66 | } |
| 67 | |
| 68 | return false; |
| 69 | }; |
| 70 | |
| 71 | const xWins = wins('X'); |
| 72 | const oWins = wins('O'); |
| 73 | |
| 74 | // Validate turn order and game state |
| 75 | |
| 76 | // If someone wins, check if the game was valid |
| 77 | if (xWins || oWins) { |
| 78 | // If both players win, it's impossible |
| 79 | if (xWins && oWins) { |
| 80 | throw new Error('Impossible board: game should have ended after the game was won'); |
| 81 | } |
| 82 | |
| 83 | // If X wins |
| 84 | if (xWins) { |
| 85 | // Check if O continued playing after X won |
| 86 | // X wins on their nth move, so O should have at most (n-1) moves |
| 87 | // If O has made as many or more moves than X, the game continued after X won |
| 88 | if (countO >= countX) { |
| 89 | throw new Error('Impossible board: game should have ended after the game was won'); |
| 90 | } |
| 91 | return 'win'; |
| 92 | } |
| 93 | |
| 94 | // If O wins |
| 95 | if (oWins) { |
| 96 | // Check if X continued playing after O won |
| 97 | // O wins on their nth move, so X should have at most n moves |
| 98 | // If X has made more moves than O, the game continued after O won |
| 99 | if (countX > countO) { |
| 100 | throw new Error('Impossible board: game should have ended after the game was won'); |
| 101 | } |
| 102 | return 'win'; |
| 103 | } |
| 104 | } |
| 105 | |
| 106 | // Now validate turn order for non-winning games |
| 107 | // Edge Case: Invalid turn order - O started the game (O has moves but X has none) |
| 108 | if (countO > 0 && countX === 0) { |
| 109 | throw new Error('Wrong turn order: O started'); |
| 110 | } |
| 111 | |
| 112 | // Edge Case: Invalid turn order - O has too many moves (O went twice) |
| 113 | if (countO > countX) { |
| 114 | throw new Error('Wrong turn order: O went twice'); |
| 115 | } |
| 116 | |
| 117 | // Edge Case: Invalid turn order - X has more than one extra move |
| 118 | if (countX > countO + 1) { |
| 119 | throw new Error('Wrong turn order: X went twice'); |
| 120 | } |
| 121 | |
| 122 | // Determine game state for non-winning boards |
| 123 | // Edge Case: Board is full with no winner (draw) |
| 124 | if (countX + countO === 9) { |
| 125 | return 'draw'; |
| 126 | } |
| 127 | |
| 128 | // Edge Case: Game is not finished yet (ongoing) |
| 129 | return 'ongoing'; |
| 12 | 130 | }; |