算法 6.20
void Coding( HuffmanTree T，i，Stack &S) {
  if (T) {
     if ( (T.Tree[i].lchild==-1) && (T.Tree[i].rchild==-1) ) {
       *HC[i] = new char[StackLength(S)];
       StackTraverse(S);        // 從棧底到棧頂將棧中字符復制到HC[i]中
     }//if
     Push(S, '0');
     Coding( T, T.Tree[i].lchild, S );
     Pop(S, e);
     Push(S, '1');
     Coding( T, T.Tree[i].rchild, S );
     Pop(S, e);
   }//if
}//Coding