C :

#include <stdlib.h>
void root( char *mid, char *last )
{
    char a,*x,*y;

    if(!*mid)
        return; 
    x= last+strlen(last)-1;
    printf("%c",*x);

    y=strchr(mid,*x);    
    *x=0x0;
    x=y-mid+last;
    a=*x;
    *x=0x0;
    *y=0x0;
	root(mid,last);
    *x=a;
    root( y+1,x);
}


int main()
{
    char mid[50];
    char last[50];
	scanf("%s%*c%s%*c",mid,last);
	root(mid,last);
    printf( "\n" );

    return 0;
}

C++ :

#include <iostream>
#include <string.h>
using namespace std;
void build(int n,char* s1,char* s2){
	if(n<=0)	return;
	int p=strchr(s2,s1[n-1])-s2;
	cout<<s1[n-1];
	build(p,s1,s2);
	build(n-1-p,s1+p,s2+p+1);
}
int main()
{
	char s1[100],s2[100];
	while(cin>>s2>>s1)
	{
		int n=strlen(s1);
		build(n,s1,s2);
		cout<<endl;
	}
	return 0;
}

Pascal :

var s1,s2:string;
procedure dfs(mid,last:string); 
var root:string;i:longint; 
begin
  if (mid='')and(last='') then exit; 
  root:=last[length(last)]; 
  write(root); 
  for i:=1 to length(last) do
    if mid[i]=root then break; 
  dfs(copy(mid,1,i-1),copy(last,1,i-1)); 
  dfs(copy(mid,i+1,length(mid)-i),copy(last,i,length(last)-i));
end; 
begin
  readln(s1); 
  readln(s2);
  dfs(s1,s2); 
  writeln;
end.