1
class Solution {
2
  public boolean validTicTacToe(String[] board) {
3
    // cnt number of X and O
4
    int x = cntNumber('X', board);
5
    // this check can be omitted, it can be covered in the second number check.
6
    if (x > 5) {
7
      return false;
8
    }
9
    int o = cntNumber('O', board);
10
    if (x < o || x > o + 1) {
11
      return false;
12
    }
13
    // if(x <3 ) true, no need to see winning
14
    if (o >= 3) {
15
      // if x has won, but game doesnt stop
16
      if (x == o && hasWon('X', board)) {
17
        return false;
18
      }
19
      // if o has won, but game doesnt stop
20
      if (x > o && hasWon('O', board)) {
21
        return false;
22
      }
23
    }
24
    return true;
25
  }
26

27
  private int cntNumber(char target, String[] board) {
28
    int res = 0;
29
    for (int i = 0; i < 3; i++) {
30
      for (int j = 0; j < 3; j++) {
31
        if (target == board[i].charAt(j)) {
32
          res++;
33
        }
34
      }
35
    }
36
    return res;
37
  }
38

39
  private boolean hasWon(char target, String[] board) {
40
    String toWin = Character.toString(target).repeat(3);
41
    for (int i = 0; i < 3; i++) {
42
      if (board[i].equals(toWin)) {
43
        return true;
44
      }
45
    }
46
    for (int j = 0; j < 3; j++) {
47
      boolean col = true;
48
      for (int i = 0; i < 3; i++) {
49
        col = col && target == board[i].charAt(j);
50
        if (!col) {
51
          break;
52
        }
53
      }
54
      if (col) {
55
        return true;
56
      }
57
    }
58
    // check diagonal. If center is not target, not possible to form diag win.
59
    if (target != board[1].charAt(1)) {
60
      return false;
61
    }
62

63
    boolean diagonal1 = target == board[0].charAt(0);
64
    // only proceed if the first letter match. Otherwise might get false positive
65
    if (diagonal1) {
66
      if (target == board[2].charAt(2)) {
67
        return true;
68
      }
69
    }
70

71
    boolean diagonal2 = target == board[0].charAt(2);
72
    if (diagonal2) {
73
      if (target == board[2].charAt(0)) {
74
        return true;
75
      }
76
    }
77
    return false;
78
  }
79
}