Valid tic tac toe state

/*
 * Given a Tic-Tac-Toe board 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 that 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 three 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 = ["XOX","O O","XOX"]
 * Output: true
 * Constraints:
 * board.length == 3
 * board[i].length == 3
 * board[i][j] is either 'X', 'O', or ' '.
 */
impl Solution {
  pub fn valid_tic_tac_toe(board: Vec<String>) -> bool {
    let b: Vec<Vec<char>> = board.iter().map(|s| s.chars().collect()).collect();
    let count_x = b.iter().flatten().filter(|&&c| c == 'X').count() as i32;
    let count_o = b.iter().flatten().filter(|&&c| c == 'O').count() as i32;

    if count_x != count_o && count_x != count_o + 1 { return false; }

    let wins = |p: char| -> bool {
      for i in 0..3 {
        if b[i].iter().all(|&c| c == p) { return true; }
        if (0..3).all(|j| b[j][i] == p) { return true; }
      }
      if (0..3).all(|i| b[i][i] == p) { return true; }
      if (0..3).all(|i| b[i][2-i] == p) { return true; }
      false
    };
    let x_wins = wins('X');
    let o_wins = wins('O');

    if x_wins && o_wins { return false; }
    if x_wins && count_x != count_o + 1 { return false; }
    if o_wins && count_x != count_o { return false; }
    true
  }
}