Coursera_algorithm/Percolation.java at master · TengHu/Coursera_algorithm · GitHub

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public class Percolation
{

	private static boolean[] grid;
	private static int N;
	private UF uf;

	public Percolation(int N)// create N-by-N grid, with all sites blocked
	{
		this.N = N;

		this.grid = new boolean[N*N + 2];

		this.grid[0] = true;
		this.grid[N*N + 1] = true;
		for(int i = 1; i<= N*N; i++)
		{
			grid[i] = false;
		}

		this.uf = new UF(N*N+2);

		for(int i = 1; i <= N; i++)
		{
   			this.uf.union(0,i);
		}

		for(int i = 1; i <= N; i++)
		{
   			this.uf.union(N*N+1,N*(N-1)+i);
		}
	}

	public void open(int i,int j)
	{
		grid[N * (i - 1) + j] = true;

		if( i == 1 && j == 1)
		{
			if( grid[ N * (i) + j ] == true ) uf.union(N * (i - 1) + j , N * (i) + j);//down
			if( grid[ N * (i - 1) + j + 1] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j + 1);//right
		}else if( i == 1 && j == N)
		{
			if( grid[ N * (i - 1) + j - 1] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j - 1);//left
			if( grid[ N * (i) + j ] == true ) uf.union(N * (i - 1) + j , N * (i) + j);//down
		}else if( i == N && j == 1)
		{
			if( grid[ N * (i - 2) + j ] == true ) uf.union(N * (i - 1) + j , N * (i - 2) + j);//up
			if( grid[ N * (i - 1) + j + 1 ] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j + 1);//right
		}else if( i == N && j == N)
		{
			if( grid[ N * (i - 2) + j ] == true ) uf.union(N * (i - 1) + j , N * (i - 2) + j);//up
			if( grid[ N * (i - 1) + j - 1] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j - 1);//left
		}else if( i == 1  )
		{
			if( grid[ N * (i) + j ] == true ) uf.union(N * (i - 1) + j , N * (i) + j);//down
			if( grid[ N * (i - 1) + j - 1] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j - 1);//left
			if( grid[ N * (i - 1) + j + 1 ] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j + 1);//right
		}
		else  if ( i == N )
		{
			if( grid[ N * (i - 2) + j ] == true ) uf.union(N * (i - 1) + j , N * (i - 2) + j);//up
			if( grid[ N * (i - 1) + j - 1] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j - 1);//left
			if( grid[ N * (i - 1) + j + 1 ] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j + 1);//right
		}else if ( j == 1)
		{
			if( grid[ N * (i) + j ] == true )  uf.union(N * (i - 1) + j , N * (i) + j);//down
			 if( grid[ N * (i - 2) + j ] == true ) uf.union(N * (i - 1) + j , N * (i - 2) + j);//up
			if( grid[ N * (i - 1) + j + 1 ] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j + 1);//right
		}else if( j == N)
		{
			if( grid[ N * (i - 2) + j ] == true ) uf.union(N * (i - 1) + j , N * (i - 2) + j);//up
			if( grid[ N * (i - 1) + j - 1] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j - 1);//left
			if( grid[ N * (i - 1) + j + 1 ] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j + 1);//right
		}else
		{
			if( grid[ N * (i - 2) + j ] == true ) uf.union(N * (i - 1) + j , N * (i - 2) + j);//up
			if( grid[ N * (i - 1) + j - 1] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j - 1);//left
			if( grid[ N * (i - 1) + j + 1 ] == true ) uf.union(N * (i - 1) + j , N * (i - 1) + j + 1);//right
			if( grid[ N * (i) + j ] == true )  uf.union(N * (i - 1) + j , N * (i) + j);//down
		}
	}

	public static boolean isOpen(int i, int j)
	{
		return grid[N * (i - 1) + j];

	}

	public void grid_display()
	{
		for(int i = 1; i <= N; i++)
		{
			for(int j = 1; j <= N; j++)
			{
				StdOut.print( grid[N * (i - 1) + j] + " " );
			}
			StdOut.println();
		}
	}


	public boolean percolates()//does the system percolate?
	{
		//StdOut.print(uf.connected(0,N*N + 1) + " ");
		//StdOut.println();
		return 	uf.connected(0,N*N + 1);
	}


	public static void main(String[] args)
	{
		/*int count = 0;
		Percolation pc = new Percolation(200);
		while( !pc.percolates())
		{
			int row = StdRandom.uniform(1,N+1);
			int column = StdRandom.uniform(1,N+1);
			if( isOpen(row,column) ) continue;
			else
			{
				StdOut.print( "row :" + row +  "column :" + column + " ");
				StdOut.println();
				pc.open(row,column);
				count++;
			}
		}
		pc.grid_display();
		StdOut.println();
		StdOut.print(count + " ");*/
	}
}