// 獲取父節(jié)點(diǎn)的索引值
public int parent(int index) {
    if (index <= 0) {
        throw new RuntimeException("Invalid Index");
    }

    return (index - 1) / 2;
}

// 獲取左孩子節(jié)點(diǎn)索引
public int leftChild(int index) {
    return index * 2 + 1;
}

// 獲取右孩子節(jié)點(diǎn)索引
public int rightChild(int index) {
    return index * 2 + 2;
}

// 添加元素
public void add(E e) {
    data.add(e);
    siftUp(data.size() - 1);
}

// siftDown
private void siftDown(int k) {
    while (leftChild(k) < data.size()) {
        int j = leftChild(k);
        if (j + 1 < data.size() && data.get(j + 1).compareTo(data.get(j)) > 0) {
            j++;
        }
        if (data.get(k).compareTo(data.get(j)) >= 0) {
            break;
        }
        Collections.swap(data, k, j);
        k = j;
    }
}

import java.util.ArrayList;
import java.util.Collections;

public class BinaryHeap<E extends Comparable<E>> {

    private ArrayList<E> data;

    // 無(wú)參構(gòu)造
    public BinaryHeap() {
        data = new ArrayList<>();
    }

    // 有參構(gòu)造
    public BinaryHeap(int capacity) {
        data = new ArrayList<>(capacity);
    }

    // 或者元素個(gè)數(shù)
    public int size() {
        return data.size();
    }

    // 判斷堆是否為空
    public boolean isEmpty() {
        return data.isEmpty();
    }

    // 獲取父節(jié)點(diǎn)的索引值
    public int parent(int index) {
        if (index <= 0) {
            throw new RuntimeException("Invalid Index");
        }

        return (index - 1) / 2;
    }

    // 獲取左孩子節(jié)點(diǎn)索引
    public int leftChild(int index) {
        return index * 2 + 1;
    }

    // 獲取右孩子節(jié)點(diǎn)索引
    public int rightChild(int index) {
        return index * 2 + 2;
    }

    // 添加元素
    public void add(E e) {
        data.add(e);
        siftUp(data.size() - 1);
    }

    // siftUp
    private void siftUp(int k) {
        while (k > 0 && data.get(parent(k)).compareTo(data.get(k)) < 0) {
            Collections.swap(data, k, parent(k));
            k = parent(k);
        }

    }

    // siftDown
    private void siftDown(int k) {
        while (leftChild(k) < data.size()) {
            int j = leftChild(k);
            if (j + 1 < data.size() && data.get(j + 1).compareTo(data.get(j)) > 0) {
                j++;
            }
            if (data.get(k).compareTo(data.get(j)) >= 0) {
                break;
            }
            Collections.swap(data, k, j);
            k = j;
        }
    }
}