Percolation.java

public class Percolation {
	private int width;
	private int count;
	private int[] sz;
	private int[] id;

//imported

    // Return the number of disjoint sets.
    public int count() {
        return count;
    }

    // Return component identifier for component containing p
    public int find(int p) {
        while (p != id[p])
            p = id[p];
        return p;
    }
    // Are objects p and q in the same set?
    public boolean connected(int p, int q) {
        return find(p) == find(q);
    }

  
   // Replace sets containing p and q with their union.
    public void union(int p, int q) {
        int i = find(p);
        int j = find(q);
        if (i == j) return;

        // make smaller root point to larger one
        if   (sz[i] < sz[j]) { id[i] = j; sz[j] += sz[i]; }
        else                 { id[j] = i; sz[i] += sz[j]; }
        count--;
    }






	public Percolation(int n) {
		count = n*n + 2;
		id = new int[n*n +2];
		sz = new int[n*n + 2];
		for (int i = 0; i < n*n + 2; i++) {
			id[i] = i;
 	  		sz[i] = 1;
		}
		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);
	}
}