Trees

Recall one of the tree definitions given in class:

     enum ABTree_Tag {IS_LEAF, IS_NODE};
     struct ABTree {
        enum ABTree_Tag  tag;
        union {
           int  leaf;
           struct {
              struct ABTree *  left;
              struct ABTree *  right;
           } node;
        } elt;
     };
     typedef  struct ABTree *  BTree;

This is for binary trees of integers, where the data are only at the leaves.