Validity of a given Tic-Tac-Toe board configuration - GeeksforGeeks
// This matrix is used to find indexes to check all
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A Tic-Tac-Toe board is given after some moves are played. Find out if the given board is valid, i.e., is it possible to reach this board position after some moves or not.
Note that every arbitrary filled grid of 9 spaces isn’t valid e.g. a grid filled with 3 X and 6 O isn’t valid situation because each player needs to take alternate turns.
// This matrix is used to find indexes to check all
// possible wining triplets in board[0..8]int win[8][3] = {{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'bool 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 falsebool isValid(char board[9]){ // 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 xount 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 'O' is not winner, then return true return true; } return false;}