最小堆实际上一颗自平衡的二叉树，数组的第一个元素就是堆顶，也是二叉树的根，第二和第三个元素分别是根的左孩子和右孩子，以此类推下去。

        最小堆有如下性质：

       1、堆顶元素永远都是最小的。

       2、父节点永远比它的两个孩子要小。       

package com.au.algorithm;

import java.lang.reflect.Array;

/**
 * 最小堆
 * 
 * @author Ayou
 * 
 * @param <T>
 */
public class MinHeap<T extends Comparable<T>> {

	private int maxSize;
	private int curSize;
	private Node[] heapArray;

	public MinHeap(int size) {
		maxSize = size;
		curSize = 0;
		heapArray = (Node[]) Array.newInstance(Node.class, maxSize);
	}

	public void push(T key) {
		if (curSize < maxSize) {
			heapArray[curSize] = new Node(key);
			filterUp(curSize);
			curSize++;
		} else {
			if (heapArray[0].key.compareTo(key) < 0) {
				heapArray[0].key = key;
				filterDown(0);
			}
		}
	}

	private void filterUp(int start) {
		Node cur = heapArray[start];
		int parentIdx = (start - 1) / 2;
		while (start > 0) {
			if (heapArray[parentIdx].key.compareTo(heapArray[start].key) < 0) {
				// 父节点的值较小，不进行调整
				break;
			} else {
				heapArray[start] = heapArray[parentIdx];
				start = parentIdx;
				parentIdx = (start - 1) / 2;
				heapArray[start] = cur;
			}
		}
	}

	private void filterDown(int start) {
		Node cur = heapArray[start];
		int childIdx = start * 2 + 1;
		while (childIdx < curSize) {
			if (childIdx < curSize - 1
					&& heapArray[childIdx].key
							.compareTo(heapArray[childIdx + 1].key) > 0) {
				// 指向值较小的孩子
				childIdx++;
			}
			if (heapArray[childIdx].key.compareTo(heapArray[start].key) > 0) {
				// 孩子节点的值较大，不进行调整
				break;
			} else {
				heapArray[start] = heapArray[childIdx];
				start = childIdx;
				childIdx = start * 2 + 1;
				heapArray[start] = cur;
			}
		}
	}

	public T pop() {
		Node cur = heapArray[0];
		heapArray[0] = heapArray[curSize - 1];
		heapArray[curSize - 1] = null;
		curSize--;
		filterDown(0);
		return cur == null ? null : cur.key;
	}

	public void printer() {
		for (Node n : heapArray) {
			if (n == null)
				break;
			System.out.print(n.key + " ");
		}
		System.out.print("\r\n");
	}

	class Node {
		private T key;

		Node(T e) {
			this.key = e;
		}
	}

	/**
	 * @param args
	 */
	public static void main(String[] args) {
		MinHeap<Integer> hp = new MinHeap<Integer>(5);

		hp.push(53);
		hp.push(17);
		hp.push(78);
		hp.push(9);
		hp.push(45);
		hp.push(65);
		hp.push(87);
		hp.push(23);
		hp.printer();

		hp.pop();
		hp.printer();

	}

}