Percolation.java

class Percolation extends WeightedQuickUnionUF {
	private int width;

	public Percolation(int n) {
		super(n * n + 2);
		for(int i = 0; i < n; i++) {
			union(1 + n * (n - 1) + i, n * n + 1);
		}
		width = n;
	}

	private int position(int i, int j) { // calculates position in 1d array
		return 1 + n * i + j;
	}

	public void open(int i, int j) { // open site (row i, column j) if it is not already
		if(i > 0) {
			union(position(i-1, j), position(i, j));
		} else {
			union(position(i-1, j), 0);
		}
		if(j > 0) {
			union(position(i, j-1), position(i, j));
		}
		if(j < width - 1) {
			union(position(i, j+1), position(i, j));
		}
	}

	public boolean isOpen(int i, int j) { // is site (row i, column j) open?
		return connected(position(i, j), i > 0 ? position(i-1, j) : 0);
	}

	public boolean isFull(int i, int j) { // is site (row i, column j) full? 
		return connected(position(i, j), 0);
	}

	public boolean percolates() {
		return connected(0, width * width + 1);
	}
}