Validity of a given Tic-Tac-Toe board configuration

// Java program to check whether a given tic tac toe 
// board is valid or not 
import java.io.*;
class GFG {

// This matrix is used to find indexes to check all 
// possible winning triplets in board[0..8] 
    static int win[][] = {{0, 1, 2}, // Check first row. 
    {3, 4, 5}, // Check second Row 
    {6, 7, 8}, // Check third Row 
    {0, 3, 6}, // Check first column 
    {1, 4, 7}, // Check second Column 
    {2, 5, 8}, // Check third Column 
    {0, 4, 8}, // Check first Diagonal 
    {2, 4, 6}}; // Check second Diagonal 

// Returns true if character 'c' wins. c can be either 
// 'X' or 'O' 
    static boolean isCWin(char[] board, char c) {
        // Check all possible winning combinations 
        for (int i = 0; i < 8; i++) {
            if (board[win[i][0]] == c
                    && board[win[i][1]] == c
                    && board[win[i][2]] == c) {
                return true;
            }
        }
        return false;
    }

// Returns true if given board is valid, else returns false 
    static boolean isValid(char board[]) {
        // Count number of 'X' and 'O' in the given board 
        int xCount = 0, oCount = 0;
        for (int i = 0; i < 9; i++) {
            if (board[i] == 'X') {
                xCount++;
            }
            if (board[i] == 'O') {
                oCount++;
            }
        }

        // Board can be valid only if either xCount and oCount 
        // is same or count is one more than oCount 
        if (xCount == oCount || xCount == oCount + 1) {
            // Check if 'O' is winner 
            if (isCWin(board, 'O')) {
                // Check if 'X' is also winner, then 
                // return false 
                if (isCWin(board, 'X')) {
                    return false;
                }

                // Else return true xCount and yCount are same 
                return (xCount == oCount);
            }

            // If 'X' wins, then count of X must be greater 
            if (isCWin(board, 'X') && xCount != oCount + 1) {
                return false;
            }

            // If 'O' is not winner, then return true 
            return true;
        }
        return false;
    }

// Driver program 
    public static void main(String[] args) {
        char board[] = {'X', 'X', 'O', 'O', 'O', 'X', 'X', 'O', 'X'};

        if ((isValid(board))) {
            System.out.println("Given board is valid");
        } else {
            System.out.println("Given board is not valid");
        }
    }
}
//this code contributed by PrinciRaj1992

import java.util.Arrays;

public class TicTacToe {
    
    // Returns true if character 'c' wins. c can be either 'X' or 'O'
    public static boolean isWinner(char[] board, char c) {
        // Check all possible winning combinations
        if ((board[0] == c && board[1] == c && board[2] == c) ||
            (board[3] == c && board[4] == c && board[5] == c) ||
            (board[6] == c && board[7] == c && board[8] == c) ||
            (board[0] == c && board[3] == c && board[6] == c) ||
            (board[1] == c && board[4] == c && board[7] == c) ||
            (board[2] == c && board[5] == c && board[8] == c) ||
            (board[0] == c && board[4] == c && board[8] == c) ||
            (board[2] == c && board[4] == c && board[6] == c))
            return true;
        
        return false;
    }

    // Returns true if given board is valid, else returns false
    public static boolean isValid(char[] board) {
        // Count number of 'X' and 'O' in the given board
        int xCount = 0, oCount = 0;
        for (int i = 0; i < 9; i++) {
            if (board[i] == 'X')
                xCount++;
            if (board[i] == 'O')
                oCount++;
        }

        // Board can be valid only if either xCount and oCount is same or count is one more than oCount
        if (xCount == oCount || xCount == oCount + 1) {
            // Check if there is only one winner
            if (isWinner(board, 'X') && isWinner(board, 'O'))
                return false;
            
            // If 'X' wins, then count of X must be greater
            if (isWinner(board, 'X') && xCount != oCount + 1)
                return false;
            
            // If 'O' wins, then count of X must be same as oCount
            if (isWinner(board, 'O') && xCount != oCount)
                return false;

            return true;
        }
        return false;
    }

    // Driver program
    public static void main(String[] args) {
        char[] board = {'X', 'X', 'O',
                        'O', 'O', 'X',
                        'X', 'O', 'X'};
        
        if (isValid(board))
            System.out.println("Given board is valid");
        else
            System.out.println("Given board is not valid");
    }
}