构造哈夫曼树

/*exp7-6.cpp*/

#include <stdio.h>

#include <string.h>
#define N 50/*叶子结点数*/
#define M 2*N-1/*树中结点总数*/
typedef struct
{
 char data[5];/*结点数*/
 int weight;/*权重*/
 int parent;/*双亲结点*/
 int lchild;/*左孩子结点*/
 int rchild;/*右孩子结点*/
}HTNode;
typedef struct
{
 char cd[N];/*存放哈夫曼码*/
 int start;
}HCode;

void CreateHT(HTNode ht[],int n)/*构造哈夫曼树*/
{
 int i,k,lnode,rnode;
 int min1,min2;
 for(i=0;i<2*n-1;i++)/*所有结点的相关域置初值-1*/
  ht[i].parent=ht[i].lchild=ht[i].rchild=-1;
 for(i=n;i<2*n-1;i++)/*构造哈夫曼树*/
 {
  min1=min2=32767;/*lnode和rnode为最小权重的两个结点的位置*/
  lnode=rnode=-1;
  for(k=0;k<=i-1;k++)
   if(ht[k].parent==-1)/*只在尚未构造二叉树的结点中查找*/
   {
    if(ht[k].weight<min1)
    {
     min2=min1;rnode=lnode;
     min1=ht[k].weight;lnode=k;
    }
    else if(ht[k].weight<min2)
    {
     min2=ht[k].weight;rnode=k;
    }
   }
   ht[lnode].parent=i;ht[rnode].parent=i;
   ht[i].weight=ht[lnode].weight+ht[rnode].weight;
   ht[i].lchild=lnode;ht[i].rchild=rnode;
 }
}

void CreateHCode(HTNode ht[],HCode hcd[],int n)/*构造哈夫曼编码*/
{
 int i,f,c;
 HCode hc;
 for(i=0;i<n;i++)/*根据哈夫曼树求哈夫曼编码*/
 {
  hc.start=n;c=i;
  f=ht[i].parent;
  while(f!=-1)/*循序直到树根结点*/
  {
   if(ht[f].lchild==c)/*处理左孩子结点*/
    hc.cd[hc.start--]='0';
   else/*处理右孩子结点*/
    hc.cd[hc.start--]='1';
   c=f;f=ht[f].parent;
  }
  hc.start++;/*start指向哈夫曼编码最开始字符*/
  hcd[i]=hc;
 }
}

void DispHCode(HTNode ht[],HCode hcd[],int n)/*输出哈夫曼编码*/
{
 int i,k;
 int sum=0,m=0,j;
 printf("输出哈夫曼编码：\n");/*输出哈夫曼编码*/
 for(i=0;i<n;i++)
 {
  j=0;
  printf("  %s:\t",ht[i].data);
  for(k=hcd[i].start;k<=n;k++)
  {
   printf("%c",hcd[i].cd[k]);
   j++;
  }
  m+=ht[i].weight;
  sum+=ht[i].weight*j;
  printf("\n");
 }
 printf("\n平均长度=%g\n",1.0*sum/m);
}

void main()
{
 int n=15,i;
 char *str[]={"The","of","a","to","and","in","that","he","is","at",
 "on","for","His","are","be"};
 int fnum[]={1192,677,541,518,462,450,242,195,190,181,174,157,138,124,123};
 HTNode ht[M];
 HCode hcd[N];
 for(i=0;i<n;i++)
 {
  strcpy(ht[i].data,str[i]);
  ht[i].weight=fnum[i];
 }
 printf("\n");
 CreateHT(ht,n);
 CreateHCode(ht,hcd,n);
 DispHCode(ht,hcd,n);
 printf("\n");
}