大根堆和小根堆

来源：互联网发布：注册淘宝网店编辑：程序博客网时间：2024/05/22 03:23

先看一下调整好的小根堆和大根堆

下面举一个调整的例子

下面是一个实际的问题：数据流中的中位数
题目描述：

如何得到一个数据流中的中位数？如果从数据流中读出奇数个数值，那么中位数就是所有数值排序之后位于中间的数值。如果从数据流中读出偶数个数值，那么中位数就是所有数值排序之后中间两个数的平均值。

import java.util.ArrayList;public class BuilderHeap {void adjustMaxHeap(ArrayList<Integer> array, int parent) {// array[0 ~ size-1]int lchild = 2 * parent + 1;int rchild = 2 * parent + 2;int max = parent;int size = array.size();if (parent < size / 2) {if (lchild < size && array.get(lchild) > array.get(max))max = lchild;if (rchild < size && array.get(rchild) > array.get(max))max = rchild;if (max != parent) {int tmp = array.get(parent);array.set(parent, array.get(max));array.set(max, tmp);adjustMaxHeap(array, max);}}}void adjustMinHeap(ArrayList<Integer> array, int parent) {// array[0 ~ size-1]int lchild = 2 * parent + 1;int rchild = 2 * parent + 2;int min = parent;int size = array.size();if (parent < size / 2) {if (lchild < size && array.get(lchild) < array.get(min))min = lchild;if (rchild < size && array.get(rchild) < array.get(min))min = rchild;if (min != parent) {int tmp = array.get(parent);array.set(parent, array.get(min));array.set(min, tmp);adjustMaxHeap(array, min);}}}ArrayList<Integer> minArray = new ArrayList<>();ArrayList<Integer> maxArray = new ArrayList<>();public void Insert(Integer num) {if (((minArray.size() + maxArray.size()) & 1) == 1) { // 已经插入奇数个if (minArray.size() + maxArray.size() >= 3) {if (num > maxArray.get(0)) { // insert into maxArrayminArray.add(maxArray.get(0));// update maxmaxArray.set(0, num);adjustMinHeap(maxArray, 0);} else { // insert into minArrayminArray.add(num);}// update minArrayfor (int i = minArray.size() / 2 - 1; i >= 0; --i) {adjustMaxHeap(minArray, i);}} else {if (num > maxArray.get(0)) { // insert into maxArrayminArray.add(maxArray.get(0));// update maxmaxArray.set(0, num);} else { // insert into minArrayminArray.add(num);}}} else { // 已经插入偶数个if (minArray.size() + maxArray.size() >= 2) {if (num > minArray.get(0)) { // insert into maxArray// update maxmaxArray.add(num);} else {maxArray.add(minArray.get(0));minArray.set(0, num);adjustMaxHeap(minArray, 0);}// update maxArrayfor (int i = maxArray.size() / 2 - 1; i >= 0; --i) {adjustMinHeap(maxArray, i);}} else {maxArray.add(num);}}}public Double GetMedian() {if (((minArray.size() + maxArray.size()) & 1) == 1) { // 已经插入奇数个return 1.0 * maxArray.get(0);} else if (maxArray.size() + minArray.size() > 0) {return (maxArray.get(0) + minArray.get(0)) / 2.0;}return 0.0;}public static void main(String[] args) {BuilderHeap heap = new BuilderHeap();int[] vals = new int[] { 5, 2, 3, 4, 1, 6, 7, 0, 8 };for (int i = 0; i < vals.length; ++i) {heap.Insert(vals[i]);System.out.println(heap.maxArray);System.out.println(heap.minArray);System.out.println(heap.GetMedian());}}}

0 0