Valid Tic-Tac-Toe State


#1

A Tic-Tac-Toe board is given as a string array board. Return True if and only if it is possible to reach this board position during the course of a valid tic-tac-toe game.

The board is a 3 x 3 array, and consists of characters " ", "X", and "O".  The " " character represents an empty square.

Here are the rules of Tic-Tac-Toe:

  • Players take turns placing characters into empty squares (" ").
  • The first player always places "X" characters, while the second player always places "O" characters.
  • "X" and "O" characters are always placed into empty squares, never filled ones.
  • The game ends when there are 3 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.
Example 1:
Input: board = ["O  ", "   ", "   "]
Output: false
Explanation: The first player always plays "X".

Example 2:
Input: board = ["XOX", " X ", "   "]
Output: false
Explanation: Players take turns making moves.

Example 3:
Input: board = ["XXX", "   ", "OOO"]
Output: false

Example 4:
Input: board = ["XOX", "O O", "XOX"]
Output: true

Note:

  • board is a length-3 array of strings, where each string board[i] has length 3.
  • Each board[i][j] is a character in the set {" ", "X", "O"}.

#2

The code below checks for the following,

  1. If both X and 'O` win, we return false.
  2. If X wins and O still plays after that, return false.
  3. If O wins and X-O count not equal to 1, return false
func validTicTacToe(board []string) bool {
    xCount, oCount := 0, 0
    xs, cs := 0, 0
    for i:=0;i<len(board);i++{
        if board[i]=="XXX" {
            xs++
        }else if board[i]=="OOO"{ 
            cs++
        }
        yax := string([]byte{board[0][i],board[1][i],board[2][i]})
        if yax=="XXX" {
            xs++
        } else if yax=="OOO" {
            cs++ 
        }
        for _, ch := range board[i]{
            if ch=='X'{ 
                xCount++
            } else if ch=='O'{
                oCount++
            }
        }
    }
    if oCount>xCount || xCount-oCount>1{ return false }
    
    dg1 := string([]byte{board[0][0],board[1][1],board[2][2]})
    dg2 := string([]byte{board[0][2],board[1][1],board[2][0]})
    if dg1=="XXX" || dg2=="XXX" {
        xs++
    } else if dg1 == "OOO" || dg2=="OOO" {
        cs++
    }
       
    if ((cs>0 && xs>0) || (xs>0 && xCount!=oCount+1) || (cs>0 && xCount!=oCount)){ return false }

    return true
}