Algorithms and Data Structures

N.Wirth. Algorithms and Data Structures. Oberon version 156
the empty subtree. Consider, for example, the binary tree shown in Fig. 4.26 and the insertion of the name
Paul. The result is shown in dotted lines in the same picture.
NORMA 2
GEORGE 1
ER 2
NIL
ANN
5 MARY 3 PAUL 1 WALTER 4
NIL
NIL NIL
NIL NIL
NIL NIL
Fig. 4.26. Insertion in ordered binary tree
The search process is formulated as a recursive procedure. Note that its parameter p is a variable
parameter and not a value parameter. This is essential because in the case of insertion a new pointer value
must be assigned to the variable which previously held the value NIL. Using the input sequence of 21
numbers that had been used above to construct the tree of Fig. 4.23, the search and insertion procedure
yields the binary tree shown in Fig. 4.27, with a call search(k, root) for each key k, where root is a
variable of type Node.
7 9
8
3
2 5
11
10 15
1 4 6
13
19
12
14 17
20
16 18
21
Fig. 4.27. Search tree generated by preceding program
PROCEDURE PrintTree (t: Node; h: INTEGER); (* ADenS443_Tree *)
VAR i: INTEGER;
BEGIN (*print tree t with indentation h*)
IF t # NIL THEN
PrintTree(t.left, h+1);
FOR i := 1 TO h DO Texts.Write(W, TAB) END;
Texts.WriteInt(W, t.key, 6); Texts.WriteLn(W);
PrintTree(t.right, h+1)
END
END PrintTree;