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Study notes · Data structures · DICT

Data Structures

Know what each structure is good at and what it costs. Exam items usually ask you to simulate operations (push/pop, enqueue/dequeue, insertions into a tree) or to choose the right structure.

2023 FAQ (copy)Scope: Arrays, stacks, queues, linked lists, trees, searching.

§1 Core structures

Structure	Order / shape	Typical costs
Array	Contiguous, indexed	Access O(1); insert in middle O(n)
Linked list	Nodes with next pointers	Insert at head O(1); search O(n)
Stack	LIFO	push/pop O(1)
Queue	FIFO	enqueue/dequeue O(1)
Binary search tree	Left < node < right	Search O(log n) if balanced, O(n) worst case
Hash table	Key → bucket	Average O(1) lookup

§2 Tree traversals

§3 Searching and sorting

§4 Worked examples

Example 1

Evaluate the postfix expression 6 2 / 3 +.

Push 6, push 2.
'/' pops 2 and 6 → 6 / 2 = 3; push 3.
Push 3. '+' pops → 3 + 3 = 6.

Answer 6

! Common traps

Popping operands in the wrong order for − and /.
Running binary search on unsorted data.

Coverage source: 2023 ICT Proficiency Certification Examination FAQs (file dated 14 Feb 2023) (third-party copy)