B2.2 Data structures: notes and practice

What you need to know

Our summary of the topic in our own words, not the IB guide.

• Distinguish static from dynamic data structures
• Compare static and dynamic structures on memory use, flexibility and access speed
• Choose a static or dynamic structure for a described scenario and justify it
• Create, index, update and iterate over a one-dimensional array or list
• Write code that searches or accumulates over a list
• Create and traverse a two-dimensional array or list, including by row and by column
• Trace code that manipulates an array or list and state the final contents
• Explain the last in, first out behaviour of a stack and name its operations
• Trace a sequence of push and pop operations and state the stack contents at the end
• Identify a problem that a stack solves naturally and explain why
• Explain the first in, first out behaviour of a queue and name its operations
• Trace a sequence of enqueue and dequeue operations and state the queue contents at the end
• Identify a problem that a queue solves naturally and explain why
• Use a dictionary or map to store and retrieve values by key

Learn it

• Create a list; index; length

  Lesson with 5 exercises

• Update, add, remove

  Lesson with 5 exercises

• Loop over a list two ways

  Lesson with 5 exercises

• Accumulate over a list

  Lesson with 4 exercises

• Search a list; find the largest without built-ins

  Lesson with 3 exercises

• Trace list code and state the final contents

  Lesson with 3 exercises

• Fixed-size arrays versus growable lists

  Lesson with 2 exercises

• Two-dimensional lists: rows and columns

  Lesson with 4 exercises

• Stack: push, pop, last in first out

  Lesson with 5 exercises

• A problem a stack solves

  Lesson with 2 exercises

• Queue: enqueue, dequeue, first in first out

  Lesson with 3 exercises

• A problem a queue solves

  Lesson with 2 exercises

• Capstone: read record lines, split, report

  Lesson with 1 exercise

Practice questions

Original questions written for the 2027 course, marked as you go. Easiest first.

• Count above a limitCoding · Warm-up
• Full array of timesWritten · Warm-up
• Last valueCoding · Warm-up
• Queue in wordsWritten · Warm-up
• Stack in wordsWritten · Warm-up
• Trace: list indexTrace table · Warm-up
• Trace: list index (Java)Trace table · Warm-up
• The averageCoding · Core
• Count up in a listCoding · Core
• Down the diagonalCoding · Core
• Double every valueCoding · Core
• First repeat in a rowCoding · Core
• Position of the largestCoding · Core
• Messages sent offlineWritten · Core
• Middle valueCoding · Core
• Move the first to the endCoding · Core
• Seats or waiting listWritten · Core
• Largest minus smallestCoding · Core
• What is left on the stackCoding · Core
• Swap the endsCoding · Core
• Tasks on holdWritten · Core
• Trace: double loopTrace table · Core
• Trace: double loop (Java)Trace table · Core
• Trace: list changesTrace table · Core
• Trace: list changes (Java)Trace table · Core
• Trace: queue movesTrace table · Core
• Trace: queue moves (Java)Trace table · Core
• Trace: running totalTrace table · Core
• Trace: running total (Java)Trace table · Core
• Trace: stack movesTrace table · Core
• Trace: stack moves (Java)Trace table · Core
• Is it an index?Coding · Core
• Do the brackets match?Coding · Stretch
• Trace table: bracket checker with a stackTrace table · Stretch
• Biggest riseCoding · Stretch
• Where it appearsCoding · Stretch
• Questions everyone got rightCoding · Stretch
• Take turns on the consoleCoding · Stretch
• The top of a small stackCoding · Stretch
• Trace: carry largerTrace table · Stretch
• Trace: carry larger (Java)Trace table · Stretch
• Trace: column totalsTrace table · Stretch
• Trace: column totals (Java)Trace table · Stretch
• Trace: swap passTrace table · Stretch
• Balanced bracketsCoding · Stretch
• Warmest dayCoding · Stretch

Exam tips for B2.2

• Draw the structure after each operation when tracing a stack or a queue.
• For a 2D list, be clear whether you loop by row first or by column first.
• Explain why a stack suits undo or bracket matching and a queue suits waiting in order.