題目 : 給中序  後序  求 前序

作法來自於 ACM 536 Tree Recovery 改編

/******************************************************/

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
int pos_tail,top;
char pos[50],in[50],pre[50];
void print(int from,int end)
{
    int i;
    if(from>end) return;
    else
        {
           pos_tail--;
           for(i=0;in[i]!='\0';i++)
               if(pos[pos_tail]==in[i])
                  {                    
                     print(i+1,end);
                     print(from,i-1);
                     pre[top++]=in[i];
                     break;
                  }
        }
}
main()
{
  while(scanf("%s %s",in,pos)==2)
       {
           pos_tail=strlen(in);
           top=0;
           print(0,strlen(in)-1);
          
           int i;
           for(i=top-1;i>=0;i--)
              printf("%c",pre[i]);
           puts("");
       }
 return 0;
}
/*
ABCDEFG
ACBFGED
*/