rendezvous with cassidoo #186 - Interview question of the week

validTTTPosition.js

/**
 * From: https://buttondown.email/cassidoo/archive/37ac19b1-2bea-4354-8860-3fdb47e456cd
 * @param {string[]} board A Tic Tac Toe board
 * @returns {boolean} If and only if it’s possible to reach this board position during the course of a valid tic-tac-toe game.
 * @example
 * const board = ["XOX", "O O", "XOX"]
 * 
 * $ validTTTPosition(board)
 * -> true
 */
function validTTTPosition (board) {
    let count = {}
    for (let y = 0; y < board.length; y++)
        for (let x = 0; x < board[y].length; x++) {
            const char = board[y][x]
            if (char === " ") continue
            count[char] = count[char] + 1 || 1
            for (let a = 0, b = 1; b>=0; b-=a>=b, a+=a<b)
                for (let l = 1; board[y+l*a]?.[x+l*b] === char; l++)
                    if (count.wins = count.wins + (l === 2) || 1 > 1) return false
        }
    return !(Math.abs((count.X||0) - (count.O||0) - .5) >= 1)
}