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Copy pathMaxHeap.java
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155 lines (139 loc) · 2.93 KB
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package heap.base;
import java.util.ArrayList;
import java.util.PriorityQueue;
public class MaxHeap {
ArrayList<Integer> list = null;
public MaxHeap() {
list = new ArrayList<>();
}
/**
* 堆长度
*
* @return
*/
public int getSize() {
return list.size();
}
/**
* 判空
*
* @return
*/
public boolean isEmpty() {
return list.isEmpty();
}
/**
* 取堆顶
*
* @return
*/
public int peek() {
if (isEmpty()) {
throw new IllegalArgumentException("max heap has no data");
}
return list.get(0);
}
/**
* 左孩子index
*
* @param index
* @return
*/
public int leftChildIndex(int index) {
return 2 * index + 1;
}
/**
* 右孩子index
*
* @param index
* @return
*/
public int rightChildIndex(int index) {
return 2 * index + 2;
}
/**
* 父节点值
*
* @param index
* @return
*/
public int perent(int index) {
return list.get(perentIndex(index));
}
/**
* 父节点index
*
* @param index
* @return
*/
public int perentIndex(int index) {
return (index - 1) / 2;
}
private void swap(int i, int j) {
int t = list.get(i);
list.set(i, list.get(j));
list.set(j, t);
}
/**
* 添加
*
* @param value
*/
public MaxHeap add(int value) {
list.add(value);
siftUp(list.size() - 1);
return this;
}
/**
* 向上构造堆
*
* @param current
*/
private void siftUp(int current) {
while (current > 0 && list.get(current) > perent(current)) {
swap(current, perentIndex(current));
current = perentIndex(current);
}
}
/**
* 向下构造堆
*
* @param current
*/
private void siftDown(int current) {
int left = leftChildIndex(current);
while (left < list.size()) {
if ((left + 1) < list.size() && list.get(left) < list.get(left + 1)) {
left = left + 1;
}
if (list.get(left) > list.get(current)) {
swap(left, current);
current = left;
left = leftChildIndex(current);
} else {
break;
}
}
}
/**
* 删除堆顶
*
* @return
*/
public int pop() {
if (isEmpty()) {
throw new IllegalArgumentException("max heap has no data");
}
if (list.size() == 0) {
int result = list.get(0);
list.remove(0);
return result;
} else {
int result = list.get(0);
list.set(0, list.get(list.size() - 1));
list.remove(list.size() - 1);
siftDown(0);
return result;
}
}
}