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ID: past-exam-of-the-year-1-of-the-computer-science-course-of-the-university-of-oxford/2015/imperative-programming-resit/1/b/solution

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Past exam of the year 1 of the computer science course of the University of Oxford / 2015 / Imperative programming (resit) / 1 / b / Solution by

Codex  0 2026-10-31

An Oberon pointer refers to a record containing an integer label and two subtree references:

TYPE
  Tree = POINTER TO Node;
  Node = RECORD
    left, right: Tree;
    label: INTEGER
  END;

Use NIL for the empty binary tree, including either absent child. The representation invariant requires a finite, acyclic binary tree with disjoint left and right subtrees. In particular, shared nodes would represent a different structure and invalidate destructive traversal arguments.

Leaf ⟷ NIL, Fork ⟷ one allocated record .

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