Java语言实现最大堆代码示例

最大堆

最大堆的特点是父元素比子元素大，并且是一棵完全二叉树。

data[1]开始存，data[0]空着不用。也可以把data[0]当成size来用。

public class MaxHeap<T extends Comparable<? super T>> {
private T[] data;
private int size;
private int capacity;
public MaxHeap(int capacity) {
this.data = (T[]) new Comparable[capacity + 1];
size = 0;
this.capacity = capacity;
}
public int size() {
return this.size;
}
public Boolean isEmpty() {
return size == 0;
}
public int getCapacity() {
return this.capacity;
}
/**
  * @return 查看最大根(只看不删, 与popMax对比)
  */
public T seekMax() {
return data[1];
}
public void swap(int i, int j) {
if (i != j) {
T temp = data[i];
data[i] = data[j];
data[j] = temp;
}
}
public void insert(T item) {
size++;
data[size] = item;
shiftUp(size);
}
/**
  * @return 弹出最大根(弹出意味着删除, 与seekMax对比)
  */
public T popMax() {
swap(1, size--);
shiftDown(1);
return data[size + 1];
}
/**
  * @param child 孩子节点下角标是child，父节点下角表是child/2
  */
public void shiftUp(int child) {
while (child > 1 && data[child].compareTo(data[child / 2]) > 0) {
swap(child, child / 2);
child = child / 2;
}
}
/**
  * @param a data数组中某个元素的下角标
  * @param b data数组中某个元素的下角标
  * @return 哪个元素大就返回哪个的下角标
  */
private int max(int a, int b) {
if (data[a].compareTo(data[b]) < 0) {
//如果data[b]大
return b;
//返回b
} else {
//如果data[a]大
return a;
//返回a
}
}
/**
  * @param a data数组中某个元素的下角标
  * @param b data数组中某个元素的下角标
  * @param c data数组中某个元素的下角标
  * @return 哪个元素大就返回哪个的下角标
  */
private int max(int a, int b, int c) {
int biggest = max(a, b);
biggest = max(biggest, c);
return biggest;
}
/**
  * @param father 父节点下角标是father,左右两个孩子节点的下角表分别是：father*2 和 father*2+1
  */
public void shiftDown(int father) {
while (true) {
int lchild = father * 2;
//左孩子
int rchild = father * 2 + 1;
//右孩子
int newFather = father;
//newFather即将更新，父、左、右三个结点谁大，newFather就是谁的下角标
if (lchild > size) {
//如果该father结点既没有左孩子，也没有右孩子
return;
} else if (rchild > size) {
//如果该father结点只有左孩子，没有右孩子
newFather = max(father, lchild);
} else {
//如果该father结点既有左孩子，又有右孩子
newFather = max(father, lchild, rchild);
}
if (newFather == father) {
//说明father比两个子结点都要大，表名已经是大根堆，不用继续调整了
return;
} else {
//否则，还需要继续调整堆，直到满足大根堆条件为止
swap(father, newFather);
//值进行交换
father = newFather;
//更新father的值，相当于继续调整shiftDown(newFather)
}
}
}
public static void main(String[] args) {
//创建大根堆
MaxHeap<Integer> maxHeap = new MaxHeap<Integer>(100);
//向堆里存
for (int i = 0; i < 100; i++) {
maxHeap.insert((int) (Math.random() * 100));
}
//创建数组
Integer[] arr = new Integer[100];
//从堆里取，放进数组里
for (int i = 0; i < 100; i++) {
arr[i] = maxHeap.popMax();
System.out.print(arr[i] + " ");
}
System.out.println();
}
}

最大堆：shiftDown()函数与上面不一样

public class MaxHeap<T extends Comparable<? super T>> {
private T[] data;
private int size;
private int capacity;
public MaxHeap(int capacity) {
data = (T[]) new Comparable[capacity + 1];
this.capacity = capacity;
size = 0;
}
public int size() {
return size;
}
public Boolean isEmpty() {
return size == 0;
}
public void insert(T item) {
data[size + 1] = item;
size++;
shiftUp(size);
}
/**
  * @return 弹出最大根(弹出意味着删除, 与seekMax对比)
  */
public T popMax() {
T ret = data[1];
swap(1, size);
size--;
shiftDown(1);
return ret;
}
/**
  * @return 查看最大根(只看不删, 与popMax对比)
  */
public T seekMax() {
return data[1];
}
public void swap(int i, int j) {
if (i != j) {
T temp = data[i];
data[i] = data[j];
data[j] = temp;
}
}
public void shiftUp(int k) {
while (k > 1 && data[k / 2].compareTo(data[k]) < 0) {
swap(k, k / 2);
k /= 2;
}
}
public void shiftDown(int father) {
while (2 * father <= size) {
int newFather = 2 * father;
if (newFather + 1 <= size && data[newFather + 1].compareTo(data[newFather]) > 0) {
//data[j] data[j+1]两者取大的那个
newFather = newFather + 1;
}
if (data[father].compareTo(data[newFather]) >= 0) {
break;
} else {
swap(father, newFather);
//值进行交换
father = newFather;
//newFather是(2*father)或者是(2*father+1),也就是继续shiftDown(newFather);
}
}
}
public static void main(String[] args) {
//创建大根堆
MaxHeap<Integer> maxHeap = new MaxHeap<Integer>(100);
//向堆里存
for (int i = 0; i < 100; i++) {
maxHeap.insert((int) (Math.random() * 100));
}
//创建数组
Integer[] arr = new Integer[100];
//从堆里取，放进数组里
for (int i = 0; i < 100; i++) {
arr[i] = maxHeap.popMax();
System.out.print(arr[i] + " ");
}
System.out.println();
}
}

来源：http://www.cnblogs.com/noKing/p/7954898.html