#include <stdio.h>
#include <string.h>
#include <malloc.h>
typedef struct node
{
char ch;
struct node *forward; /*链接下一节点*/
struct node *backward; /*链接前一节点*/
} CODE;
char *decode(char *ocode, int key)
{
char *ncode;
int length, count,i;
CODE *loop , *p;
length = strlen(ocode);
loop= (CODE*)malloc(length*sizeof(CODE)); /*动态分配密文环*/
for(i=0;i<length-1;i++)
{
loop[i].forward = &loop[i+1];
loop[i].backward =&loop[i-1];
}
loop[0].backward =&loop[length-1];
loop[0].forward = &loop[1];
loop[length-1].forward = loop;
loop[length-1].backward = &loop[length-2];
for(p=loop, i=0; i<length;i++)
{
/*产生密文链表*/
for(count=1;count<key; count++)
p= p->forward;
p->ch =*ocode++;
p->backward->forward =p->forward;
p->forward->backward = p->backward;
p = p->forward;
}
ncode = (char*)malloc((length+1)*sizeof(char));
for(i=0;i<length;i++)
ncode[i] =loop[i].ch;
ncode[length] = '\0';
return ncode;
}
void main()
{
char ocode[256];
int key, num=0;
printf("输入原文字符串: ");
while(num<255&&(ocode[num++]=getchar())!='\n');
ocode[(num==255)?num:num-1] ='\0';
do
{
printf("输入加密密钥:");
scanf("%d",&key);
} while(key<=1);
printf("电文的密码是: %s\n",decode(ocode,key));
}