二叉堆的实现代码

因为二叉堆满足完全二叉树，一颗高为h的完全二叉树有2^h到2^h-1个节点，那么就可以用数组来表示。




public class HeapDemo<T extends Comparable<? super T>>{
   public HeapDemo(){
       this(DEFAULT_CAPACITY);
   }
   public HeapDemo(int capacity){
       makeEmpty();
       enlargeArray(capacity);
   }
   public HeapDemo(T[] items){
      currentSize=items.length;
      array=(T[]) new Comparable[(currentSize+2)*11/10];
      int i=0;
      for (T t : items) {
        array[i++]=t;
    
    }
      buildHeap();
   }
   public void insert(T val){
       if(currentSize==array.length-1){
           enlargeArray(2*array.length-1);
       }
       int hole=++currentSize;
       for(array[0]=val;val.compareTo(array[hole/2])<0;hole/=2){
           array[hole]=array[hole/2];
       }
       array[hole]=val;
   }
   public T findMin(){
       return array[1];
   }
   public T deleteMin() {
        if(isEmpty()){
            throw new  RuntimeException("堆为空");
        }
        T minnum=findMin();
        array[1]=array[currentSize--];
        percolateDown(1);
        return minnum;
   }
   public  boolean isEmpty(){
       return currentSize==0;
   }
   public void makeEmpty(){
       for(int i=0;i<currentSize;i++){
           array[currentSize]=null;
       }
       currentSize=0;
   }
   private static final int DEFAULT_CAPACITY=10;
   private int currentSize;
   private T[] array;
   private void percolateDown(int hole){
       T tep=array[1];
     
       for(int child=1;hole*2<currentSize;hole=child){
           child=hole*2;
           if(array[child].compareTo(array[child+1])<0)
               child++;
           if(tep.compareTo(array[child])<0){
               array[hole]=array[child];
           }else{
               break;
           }
       }
       array[hole]=tep;
   }
   private void buildHeap(){
       for(int i=currentSize/2;i>0;i--){
           percolateDown(i);
       }
   }
   private void enlargeArray(int newSize){
       T[] oldArray=array;
       if(newSize<currentSize){
           return;
       }
       array=(T[]) new Object[newSize];
       for(int i=1;i<currentSize;i++){
           array[i]=oldArray[i];
       }
   }
}