堆操作

Comparator接口

package MyInterface;

public interface Comparator<T> {
	int compare(T x, T y);
}

package Heap;

import MyInterface.Comparator;

public class Greater<T> implements Comparator<T> {

	public int compare(T x, T y) {
		return -((Comparable<T>)x).compareTo(y);
	}
}

package Heap;

import MyInterface.Comparator;

public class Less<T> implements Comparator<T> {

	public int compare(T x, T y) {
		return ((Comparable<T>)x).compareTo(y);
	}
}

package Heap;

import MyInterface.Comparator;

public class Heaps {

	/**
	 * 建堆
	 */
	public static <T> void pushHeap(T[] arr, int last, T item,
			Comparator<? super T> comp) {

		int currPos, parentPos;
		currPos = last;
		parentPos = (currPos - 1) / 2;
		while (currPos != 0) {
			if (comp.compare(item, arr[parentPos]) < 0) {
				arr[currPos] = arr[parentPos];
				currPos = parentPos;
				parentPos = (currPos - 1) / 2;
			} else
				break;
		}
		arr[currPos] = item;
	}

	/**
	 * 删除操作
	 */
	public static <T> T popHeap(T[] arr, int last, Comparator<? super T> comp) {
		T tmp = arr[0];
		arr[0] = arr[last - 1];
		arr[last - 1] = tmp;
		adjustHeap(arr, 0, last - 1, comp);
		return tmp;
	}
	
	/**
	 * 调整堆
	 */
	private static<T> void adjustHeap(T[] arr, int first, int last, 
			Comparator<? super T> comp) {
		int currPos, childPos;
		T target;
		
		currPos = first;
		target = arr[first];
		childPos = 2 * currPos + 1;
		while(childPos < last) {
			//首先比较左右孩子大小,取大值
			if((childPos + 1 < last) &&
					comp.compare(arr[childPos + 1], arr[childPos]) < 0)
				childPos = childPos + 1;
			//再比较目标值
			if(comp.compare(arr[childPos], target) < 0) {
				arr[currPos] = arr[childPos];
				currPos = childPos;
				childPos = 2 * currPos + 1;
			}else
				break;
		}
		arr[currPos] = target;
	}
	
	/**
	 * 堆的产生
	 * 从位于索引(n-2)/2处的最后一个父结点开始，到位于索引０处的根结点结束，向上
	 * 过滤树中的每个父结点，就可以将n元素数组转换成堆.
	 */
	public static <T> void makeHeap(T[] arr, Comparator<? super T> comp) {
		int heapPos, lastPos;
		lastPos = arr.length;
		heapPos = (lastPos - 2) / 2;
		//heapPos = ((lastPos - 1) - 1) / 2;
		
		while(heapPos >= 0) {
			adjustHeap(arr, heapPos, lastPos, comp);
			heapPos--;
		}
	}
	
	/**
	 * 堆排序
	 * 最大堆以升序对数组进行排序，最小堆以降序．
	 */
	public static <T> void heapSort(T[] arr, Comparator<? super T> comp) {
		Heaps.makeHeap(arr, comp);
		int len = arr.length;
		for(int i = len; i > 1; i--) {
			Heaps.popHeap(arr, i, comp);
		}
	}
}

package Heap;

import MyInterface.Comparator;

public class TestHeap {

	public static void main(String[] args) {
		Integer[] arr = {15, 29, 52, 17, 21, 39, 8},
				  arrA = new Integer[arr.length],
				  arrB = new Integer[arr.length];
		
		Greater<Integer> greater = new Greater<Integer>();
		Less<Integer> less = new Less<Integer>();
		
		for(int i = 0; i < arr.length; i++) {
			Heaps.pushHeap(arrA, i, arr[i], greater);
			Heaps.pushHeap(arrB, i, arr[i], less);
		}
		
		//打印最大堆
		for(int i = 0; i < arrA.length; i++)
			System.out.print(arrA[i] + " "); // 52 21 39 15 17 29 8
		System.out.println();
		
		//打印最小堆
		for(int i = 0; i < arrB.length; i++)
			System.out.print(arrB[i] + " "); // 8 17 15 29 21 52 39
		
		Integer maxValue = Heaps.popHeap(arrA, arrA.length, greater);
		Integer minValue = Heaps.popHeap(arrB, arrB.length, less);
		System.out.println('\n' + "max value is: " + maxValue); // max value is: 52
		System.out.println("min value is: " + minValue); // min value is: 8
		
		// 测试堆排序
		Heaps.heapSort(arrA, greater);
		Heaps.heapSort(arrB, less);
		for (int i = 0; i < arrA.length; i++) {
			System.out.print(arrA[i] + " "); // 8 15 17 21 29 39 52
		}
		System.out.println();
		for (int i = 0; i < arrB.length; i++) {
			System.out.print(arrB[i] + " "); // 52 39 29 21 17 15 8
		}
		
	}

}