Percolations2.java

public class Percolation {
	
   private WeightedQuickUnionUF percolations;
   private boolean[] state;
   private int width;
   
   public Percolation(int N) {
	   int total = N * N;
	   width = N;
	   percolations = new WeightedQuickUnionUF(total);
	   state = new boolean[total];
	   for (int i=0; i < total; i++) {
		   state[i] = false;
	   }
   }
   
   private void validateInput(int i, int j) {
	   if (i <= 0 || i > width) {
		   throw new IndexOutOfBoundsException("row index i out of bounds");
	   }
	   if (j <= 0 || j > width) {
		   throw new IndexOutOfBoundsException("row index i out of bounds");
	   }
   }
   
   public Integer[] getNeighbouringAreas(int i, int j) {
	   Integer top, bottom, left, right;

	   if ((i - 1) <= 0) {
		   top = null;
	   } else {
		   top = getArrayPosition(i-1, j);
	   }
	   
	   if ((i + 1) > width) {
		   bottom = null; 
	   } else {
		   bottom = getArrayPosition(i+1, j);
		   
	   }
	   if ((j - 1) <= 0) {
		   left = null;
	   } else {
		   left =  getArrayPosition(i, j-1);
	   }
	   
	   if ((j + 1) > width) {
		   right = null;
	   } else {
		   right = getArrayPosition(i, j+1);
	   }
	   return new Integer[]{top, bottom, left, right};
   }
   
   private int getArrayPosition(int i, int j) {
	   return (i-1) * width + (j-1);
   }
   
   public void open(int i, int j) {
	   validateInput(i, j);
	   int myPosition = getArrayPosition(i, j);
	   state[myPosition] = true;
	   Integer[] allNeighbours = getNeighbouringAreas(i, j);
	   for (int w = 0; w < allNeighbours.length; w++) {
		   if ((allNeighbours[w] != null) && (state[allNeighbours[w]] == true)) {
			   percolations.union(allNeighbours[w], myPosition);
		   }
	   }
   }
   public boolean isOpen(int i, int j) {
	   validateInput(i, j);
	   return state[getArrayPosition(i, j)];
   }
   public boolean isFull(int i, int j) {
	   validateInput(i, j);
	   if (!isOpen(i, j)) return false;
	   
	   int myPosition = getArrayPosition(i, j);
	   for (int down=0; down < width; down++) {
		   if (isOpen(width, down+1) && percolations.connected(myPosition, getArrayPosition(width, down+1))) {
			   for (int up=0; up < width; up++) {
				   if (isOpen(1, up+1) && percolations.connected(myPosition, getArrayPosition(1, up+1))) {
					   return true;
				   }
			   }
		   }
	   }
	   return false;
   }
   public boolean percolates() {
	   for (int i=0; i < width; i++) {
		   if (isFull(width, i+1)) {
			   return true;
		   }
	   }
	   return false;
   }
}