37. 解数独

1. 步骤1 ：将所有的值保存到 列 行 3*3矩阵中
2. 步骤2 : 1~9 判断那个值可以选 可以选代入 然后回复现场

class Solution {
	boolean col[][];
	boolean row[][];
	boolean cell[][][];

	public void solveSudoku(char[][] board) {
		col = new boolean[9][9];
		row = new boolean[9][9];
		cell = new boolean[3][3][9];
		for (int i = 0; i < 9; i++) {
			for (int j = 0; j < 9; j++) {
				if (board[i][j]!= '.') {
					int t = board[i][j] - '0'-1; 							// 从 0开始数
					col[j][t] = row[i][t] = cell[i / 3][j / 3][t] = true;
				}
			}
		}
		dfs(board , 0 ,0 );
	}

	private boolean dfs(char[][] board, int x, int y) {
		if(y == 9 ) {x++;  y = 0;}
		if(x == 9) return true;
		if(board[x][y] != '.') return dfs(board , x , y+1);
		for(int i = 0 ; i < 9 ;i++) {
			if(!col[y][i]&&!row[x][i]&&!cell[x/3][y/3][i]) {
				board[x][y] = (char) ('1'+ i);
				col[y][i] = row[x][i] = cell[x / 3][y / 3][i] = true;
				if(dfs(board, x , y+1)) return true;
				board[x][y] = '.';
				col[y][i] = row[x][i] = cell[x / 3][y / 3][i] = false;

			}
		}
		return false;
	}	
}