贪心算法 哈夫曼树编码

Posted 2021-02-21 yuanqingwen

  1 #include <stdio.h>
  2 #include <string.h>
  3 #define N 50        //叶子结点数
  4 #define M 2*N-1        //树中结点总数
  5 typedef struct
  6 {
  7     char data[5];    //结点值
  8     int weight;        //权重
  9     int parent;        //双亲结点
 10     int lchild;        //左孩子结点
 11     int rchild;        //右孩子结点
 12 } HTNode;
 13 typedef struct
 14 {
 15     char cd[N];        //存放哈夫曼码
 16     int start;
 17 } HCode;
 18 void CreateHT(HTNode ht[],int n)  //由ht的叶子结点构造完整的哈夫曼树
 19 {
 20     int i,k,lnode,rnode;
 21     int min1,min2;
 22     for (i=0;i<2*n-1;i++)            //所有结点的相关域置初值-1
 23         ht[i].parent=ht[i].lchild=ht[i].rchild=-1;
 24     for (i=n;i<2*n-1;i++)            //构造哈夫曼树的分支结点
 25     {
 26         min1=min2=32767;            //lnode和rnode为最小权重的两个结点位置
 27         lnode=rnode=-1;
 28         for (k=0;k<=i-1;k++)        //查找最小和次小的结点
 29             if (ht[k].parent==-1)    //只在尚未构造二叉树的结点中查找
 30             {
 31                 if (ht[k].weight<min1)
 32                 {
 33                     min2=min1;rnode=lnode;
 34                     min1=ht[k].weight;lnode=k;
 35                 }
 36                 else if (ht[k].weight<min2)
 37                 {
 38                     min2=ht[k].weight;rnode=k;
 39                 }
 40             }
 41         ht[lnode].parent=i;ht[rnode].parent=i;    //合并两个最小和次小的结点
 42         ht[i].weight=ht[lnode].weight+ht[rnode].weight;
 43         ht[i].lchild=lnode;ht[i].rchild=rnode;
 44     }
 45 }
 46 void CreateHCode(HTNode ht[],HCode hcd[],int n)    //由哈夫曼树ht构造哈夫曼编码hcd
 47 {
 48     int i,f,c;
 49     HCode hc;
 50     for (i=0;i<n;i++)    //根据哈夫曼树构造所有叶子结点的哈夫曼编码
 51     {
 52         hc.start=n;c=i;
 53         f=ht[i].parent;
 54         while (f!=-1)    //循环直到树根结点
 55         {
 56             if (ht[f].lchild==c)    //处理左孩子结点
 57                 hc.cd[hc.start--]=‘0‘;
 58             else                    //处理右孩子结点
 59                 hc.cd[hc.start--]=‘1‘;
 60             c=f;f=ht[f].parent;
 61         }
 62         hc.start++;        //start指向哈夫曼编码最开始字符
 63         hcd[i]=hc;
 64     }
 65 }
 66 void DispHCode(HTNode ht[],HCode hcd[],int n)    //输出哈夫曼编码
 67 {
 68     int i,k;
 69     int sum=0,m=0,j;
 70     printf("输出哈夫曼编码:
"); 
 71     for (i=0;i<n;i++)
 72     {
 73         j=0;
 74         printf("      %s:	",ht[i].data);
 75         for (k=hcd[i].start;k<=n;k++)
 76         {
 77             printf("%c",hcd[i].cd[k]);
 78             j++;
 79         }
 80         m+=ht[i].weight;
 81         sum+=ht[i].weight*j;
 82         printf("
");
 83     }
 84     printf("平均长度=%g
",1.0*sum/m);
 85 }
 86 int main()
 87 {
 88     int n=6,i;
 89     char *str[]={"a","b","c","d","e","f"};
 90     int fnum[]={45,13,12,16,9,5};
 91     HTNode ht[M];
 92     HCode hcd[N];
 93     for (i=0;i<n;i++)
 94     {
 95         strcpy(ht[i].data,str[i]);
 96         ht[i].weight=fnum[i];
 97     }
 98     CreateHT(ht,n);
 99     CreateHCode(ht,hcd,n);
100     DispHCode(ht,hcd,n);
101     return 1;
102 }