照著書上給的代碼段改了一上午BUG，最後發現是書上代碼有問題。。。

 1 #include<iostream>
 2 #include<queue>
 3 using namespace std;
 4 template <class T> class Htree;
 5 template <class T>
 6 class Node{ //結點類
 7     friend class Htree<T>;
 8 public:
 9     T data;
10     Node *par;
11     Node *left;
12
 
     Node *right;
13     Node()
14     {
15         par=left=right=NULL;
16     }
17     Node(const T value,Node<T> *l,Node<T> *r)
18     {
19         data=value;
20         left=l;
21         right=r;
22     }
23     Node<T>& operator =(const Node &n)
24     {
25         data=n.data;
 
26         par=n.par;
27         left=n.left;
28         right=n.right;
29     }
30     friend const bool operator<(const Node &a,const Node &b) //重載運算符，用於優先隊列
31     {
32         return a.data>b.data;
33     }
34 };
35 template <class T>
36 class Htree{
37 public:
38     Node<T> *root;
 
39     Htree(T w[],int n)
40     {
41         priority_queue<Node<T> > heap; //小根堆，每次取出值最小的兩個結點
42         Node<T> first,second,*p,*q;
43         Node<T> *List=new Node<T>[n];
44         for(int i=0;i<n;i++)
45         {
46             List[i].data=w[i];
47             List[i].par=List[i].right=List[i].left=NULL;
48             heap.push(List[i]);
49         }
50         for(int i=0;i<n-1;i++)
51         {
52             first=(heap.top());
53             heap.pop();
54             second=(heap.top());
55             heap.pop();
56             p=new Node<T>(first.data,first.left,first.right); //取出後一定要新建結點，不然會把樹的指針變成環
57             q=new Node<T>(second.data,second.left,second.right); //同上
58             Node<T> *parent=new Node<T>(first.data+second.data,p,q); //新建一個父節點，並將前兩個結點設為子樹
59             heap.push(*parent);
60             root=parent;
61         }
62         delete [] List;
63     }
64     void PreOrder(Node<T> *r) //先序遍歷
65     {
66         if(r==NULL)return;
67         cout << r->data << " ";
68         PreOrder(r->left);
69         PreOrder(r->right);
70     }
71     void InOrder(Node<T> *r) //中序遍歷
72     {
73         if(r==NULL)return;
74         InOrder(r->left);
75         cout << r->data <<" ";
76         InOrder(r->right);
77     }
78 };
79 
80 int main()
81 {
82     int n;
83     int a[1000],s;
84     while(cin>>n)
85     {
86         for(int i=0;i<n;i++)
87         {
88             cin>>a[i];
89         }
90         Htree<int> t(a,n);
91         cout <<"preorder:"<<endl;
92         t.PreOrder(t.root);
93         cout <<endl;
94         cout <<"inorder:"<<endl;
95         t.InOrder(t.root);
96         cout <<endl;
97     }
98 }

Huffman樹 建樹方法代碼實現