Create removemin.java

Priority Queues/removemin.java

@@ -0,0 +1,120 @@
+import java.util.ArrayList;
+
+/*****************
+* Main function - 
+*
+	public static void main(String[] args) {
+		PQ pq = new PQ();
+		int choice = s.nextInt();
+		while(choice != -1) {
+			switch(choice) {
+				case 1 : // insert
+					int element = s.nextInt();
+					pq.insert(element);
+					break;
+				case 2 : // getMin
+				try {
+					System.out.println(pq.getMin());
+				} catch (PriorityQueueException e) {
+					return;
+				}
+					break;
+				case 3 : // removeMin
+				try {
+					System.out.println(pq.removeMin());
+				} catch (PriorityQueueException e) {
+					return;
+				}
+					break;
+				case 4 : // size
+					System.out.println(pq.size());
+					break;
+				case 5 : // isEmpty
+					System.out.println(pq.isEmpty());
+				default :
+						return;
+			}
+			choice = s.nextInt();
+		}
+	}
+*******************/
+
+class PriorityQueueException extends Exception {
+
+}
+
+public class PQ {
+
+	private ArrayList<Integer> heap;
+
+	public PQ() {
+		heap = new ArrayList<Integer>();
+	}
+
+	boolean isEmpty(){
+		return heap.size() == 0;
+	}
+
+	int size(){
+		return heap.size();
+	}
+
+	int getMin() throws PriorityQueueException{
+		if(isEmpty()){
+			// Throw an exception
+			throw new PriorityQueueException();
+		}
+		return heap.get(0);
+	}
+
+	void insert(int element){
+		heap.add(element);
+		int childIndex = heap.size() - 1;
+		int parentIndex = (childIndex - 1) / 2;
+
+		while(childIndex > 0){
+			if(heap.get(childIndex) < heap.get(parentIndex)){
+				int temp = heap.get(childIndex);
+				heap.set(childIndex, heap.get(parentIndex));
+				heap.set(parentIndex, temp);
+				childIndex = parentIndex;
+				parentIndex = (childIndex - 1) / 2;
+			}else{
+				return;
+			}
+		}
+	}
+
+	int removeMin()  throws PriorityQueueException {
+		if (isEmpty()) {
+			throw new PriorityQueueException();
+		}
+		int temp = heap.get(0);
+		heap.set(0, heap.get(heap.size() - 1));
+		heap.remove(heap.size() - 1);
+		int index = 0;
+		int minIndex = index;
+		int leftChildIndex = 1;
+		int rightChildIndex = 2;
+		while (leftChildIndex < heap.size()) {
+			if (heap.get(leftChildIndex) < heap.get(minIndex)) {
+				minIndex = leftChildIndex;
+			}
+			if (rightChildIndex < heap.size() && heap.get(rightChildIndex) < heap.get(minIndex)) {
+				minIndex = rightChildIndex;
+			}
+			if (minIndex == index) {
+				break;
+			} else {
+				int temp2 = heap.get(index);
+				heap.set(index, heap.get(minIndex));
+				heap.set(minIndex, temp2);
+				index = minIndex;
+				leftChildIndex = 2 * index + 1;
+				rightChildIndex = 2 * index + 2;
+			}
+		}
+		return temp;
+	}
+
+}