Valid Sukodu

Normal validation solution checking by row, column and square takes O(n^3) time, where n = 9.

This solution takes O(n^2) time, but O(n^2) space.

	public boolean isValidSudoku(char[][] board) {
		// Start typing your Java solution below
		// DO NOT write main() function
		int[][] table = new int[27][9];// 9 for each comparision: row, column, square
		int[][] square = {{0, 1, 2}, {3, 4, 5}, {6, 7, 8}};
		for(int i = 0; i < 9; i++){
			for(int j = 0; j < 9; j++){
				if(board[i][j] == '.')
					continue;
				if(board[i][j] < '1' || board[i][j] > '9')
					return false;
				int val = board[i][j] - '0';
				if(table[i][val - 1] != 0)
					return false;
				table[i][val - 1] = 1;
				if(table[j + 9][val - 1] != 0)
					return false;
				table[j + 9][val - 1] = 1;
				int squareInt = square[i / 3][j / 3];
				if(table[squareInt + 18][val - 1] != 0)
					return false;
				table[squareInt + 18][val - 1] = 1;
			}
		}
		return true;
	}