## Friday, May 6, 2016

### LeetCode 348 - Design Tic-Tac-Toe

http://www.cnblogs.com/grandyang/p/5467118.html
Design a Tic-tac-toe game that is played between two players on a n x n grid.
You may assume the following rules:
A move is guaranteed to be valid and is placed on an empty block.
Once a winning condition is reached, no more moves is allowed.
A player who succeeds in placing n of their marks in a horizontal, vertical, or diagonal row wins the game.
Example:
Given n = 3, assume that player 1 is "X" and player 2 is "O" in the board.
TicTacToe toe = new TicTacToe(3);
toe.move(0, 0, 1); -> Returns 0 (no one wins)
|X| | |
| | | | // Player 1 makes a move at (0, 0).
| | | |
toe.move(0, 2, 2); -> Returns 0 (no one wins)
|X| |O|
| | | | // Player 2 makes a move at (0, 2).
| | | |
toe.move(2, 2, 1); -> Returns 0 (no one wins)
|X| |O|
| | | | // Player 1 makes a move at (2, 2).
| | |X|
toe.move(1, 1, 2); -> Returns 0 (no one wins)
|X| |O|
| |O| | // Player 2 makes a move at (1, 1).
| | |X|
toe.move(2, 0, 1); -> Returns 0 (no one wins)
|X| |O|
| |O| | // Player 1 makes a move at (2, 0).
|X| |X|
toe.move(1, 0, 2); -> Returns 0 (no one wins)
|X| |O|
|O|O| | // Player 2 makes a move at (1, 0).
|X| |X|
toe.move(2, 1, 1); -> Returns 1 (player 1 wins)
|X| |O|
|O|O| | // Player 1 makes a move at (2, 1).
|X|X|X|
Could you do better than O(n2) per move() operation?
Hint:
Could you trade extra space such that move() operation can be done in O(1)?
You need two arrays: int rows[n], int cols[n], plus two variables: diagonal, anti_diagonal.

https://leetcode.com/discuss/101219/7-8-lines-o-1-java-python

``````public class TicTacToe {

public TicTacToe(int n) {
count = new int[6*n][3];
}

public int move(int row, int col, int player) {
int n = count.length / 6;
for (int x : new int[]{row, n+col, 2*n+row+col, 5*n+row-col})
if (++count[x][player] == n)
return player;
return 0;
}

int[][] count;
}
```

```
https://leetcode.com/discuss/101144/java-o-1-solution-easy-to-understand
In the previous solution, we allocate two arrays for player 1 and 2, respectively. Actually we can use only one array for both of the players. Say, if it is player 1 put one chess, add that location by 1. If it is player 2, deduce it by one. Finally, if either player 1 or player 2 win, that location must be equal to n or -n.

The key observation is that in order to win Tic-Tac-Toe you must have the entire row or column. Thus, we don't need to keep track of an entire n^2 board. We only need to keep a count for each row and column. If at any time a row or column matches the size of the board then that player has won.
To keep track of which player, I add one for Player1 and -1 for Player2. There are two additional variables to keep track of the count of the diagonals. Each time a player places a piece we just need to check the count of that row, column, diagonal and anti-diagonal.
private int[] rows; private int[] cols; private int diagonal; private int antiDiagonal; /** Initialize your data structure here. */ public TicTacToe(int n) { rows = new int[n]; cols = new int[n]; } /** Player {player} makes a move at ({row}, {col}). @param row The row of the board. @param col The column of the board. @param player The player, can be either 1 or 2. @return The current winning condition, can be either: 0: No one wins. 1: Player 1 wins. 2: Player 2 wins. */ public int move(int row, int col, int player) { int toAdd = player == 1 ? 1 : -1; rows[row] += toAdd; cols[col] += toAdd; if (row == col) { diagonal += toAdd; } if (col == (cols.length - row - 1)) { antiDiagonal += toAdd; } int size = rows.length; if (Math.abs(rows[row]) == size || Math.abs(cols[col]) == size || Math.abs(diagonal) == size || Math.abs(antiDiagonal) == size) { return player; } return 0; }
https://leetcode.com/discuss/101143/13-lines-simple-and-clean-o-1-java-solution
int[] rows, cols; int n, diagonal = 0, antiDiagonal = 0; public TicTacToe(int n) { this.n = n; rows = new int[n]; cols = new int[n]; } public int move(int row, int col, int player) { if(player == 1){ if(++rows[row] == n || ++cols[col] == n) return 1; if(row == col && ++diagonal == n) return 1; if(row + col == n - 1 && ++antiDiagonal == n) return 1; }else{ if(--rows[row] == -n || --cols[col] == -n) return 2; if(row == col && --diagonal == -n) return 2; if(row + col == n - 1 && --antiDiagonal == -n) return 2; } return 0; }

http://buttercola.blogspot.com/2016/06/leetcode-348-design-tic-tac-toe.html
`public` `class` `TicTacToe {`
`    ``private` `int``[][] rows;`
`    ``private` `int``[][] cols;`
`    ``private` `int``[] diag;`
`    ``private` `int``[] xdiag;`
`    ``private` `int` `n;`
`    ``/** Initialize your data structure here. */`
`    ``public` `TicTacToe(``int` `n) {`
`        ``this``.n = n;`
`        ``rows = ``new` `int``[``2``][n];`
`        ``cols = ``new` `int``[``2``][n];`
`        ``diag = ``new` `int``[``2``];`
`        ``xdiag = ``new` `int``[``2``];`
`    ``}`
`    `
`    ``/** Player {player} makes a move at ({row}, {col}).`
`        ``@param row The row of the board.`
`        ``@param col The column of the board.`
`        ``@param player The player, can be either 1 or 2.`
`        ``@return The current winning condition, can be either:`
`                ``0: No one wins.`
`                ``1: Player 1 wins.`
`                ``2: Player 2 wins. */`
`    ``public` `int` `move(``int` `row, ``int` `col, ``int` `player) {`
`        ``int` `p = player == ``1` `? ``0` `: ``1``;`
`        `
`        ``rows[p][row]++;`
`        ``cols[p][col]++;`
`        `
`        ``if` `(row == col) {`
`            ``diag[p]++;`
`        ``}`
`            `
`        ``// X-diagonal`
`        ``if` `(row + col == n - ``1``) {`
`            ``xdiag[p]++;`
`        ``}`
`            `
`        ``// If any of them equals to n, return 1`
`        ``if` `(rows[p][row] == n || cols[p][col] == n || `
`            ``diag[p] == n || xdiag[p] == n) {`
`            ``return` `p + ``1``;`
`        ``}`
`        `
`        ``return` `0``;`
`    ``}`
`}`

Not good - just different
http://dartmooryao.blogspot.com/2016/05/leetcode-348-design-tic-tac-toe.html
Map<String, Integer> map;
int n;

/** Initialize your data structure here. */
public TicTacToe(int n) {
this.n = n;
this.map = new HashMap<>();
}

/** Player {player} makes a move at ({row}, {col}).
@param row The row of the board.
@param col The column of the board.
@param player The player, can be either 1 or 2.
@return The current winning condition, can be either:
0: No one wins.
1: Player 1 wins.
2: Player 2 wins. */
public int move(int row, int col, int player) {
String rowKey = "R"+row+"_"+player;
int countR = map.getOrDefault(rowKey, 0)+1;
map.put(rowKey, countR);

String colKey = "C"+col+"_"+player;
int countC = map.getOrDefault(colKey, 0)+1;
map.put(colKey, countC);

int countD1 = 0;
if(row == col){
String d1Key = "D1_"+player;
countD1 = map.getOrDefault(d1Key, 0)+1;
map.put(d1Key, countD1);
}

int countD2 = 0;
if(row + col == n-1){
String d2Key = "D2_"+player;
countD2 = map.getOrDefault(d2Key, 0)+1;
map.put(d2Key, countD2);
}

if(countR == n || countC == n || countD1 == n || countD2 == n){
return player;
}else{
return 0;
}
}

O(n2)的解法，这种方法的思路很straightforward，就是建立一个nxn大小的board，其中0表示该位置没有棋子，1表示玩家1放的子，2表示玩家2。那么棋盘上每增加一个子，我们都每行每列，对角线和逆对角线来扫描一遍棋盘，看看是否有三子相连的情况，有的话则返回对应的玩家，没有则返回0
```    TicTacToe(int n) {
board.resize(n, vector<int>(n, 0));
}

int move(int row, int col, int player) {
board[row][col] = player;
int i = 0, j = 0, N = board.size();
for (i = 0; i < N; ++i) {
if (board[i][0] != 0) {
for (j = 1; j < N; ++j) {
if (board[i][j] != board[i][j - 1]) break;
}
if (j == N) return board[i][0];
}
}
for (j = 0; j < N; ++j) {
if (board[0][j] != 0) {
for (i = 1; i < N; ++i) {
if (board[i][j] != board[i - 1][j]) break;
}
if (i == N) return board[0][j];
}
}
if (board[0][0] != 0) {
for (i = 1; i < N; ++i) {
if (board[i][i] != board[i - 1][i - 1]) break;
}
if (i == N) return board[0][0];
}
if (board[N - 1][0] != 0) {
for (i = 1; i < N; ++i) {
if (board[N - i - 1][i] != board[N - i][i - 1]) break;
}
if (i == N) return board[N - 1][0];
}
return 0;
}
vector<vector<int>> board;```
http://stackoverflow.com/questions/22087006/using-arrays-to-detect-a-win-in-a-gomoku-game
https://github.com/javierchavez/Gomoku/blob/master/Gomoku.java