powered by v43.aiApprendre l'anatomie comme un artiste
Français
Class 9 · DSA · Enrichment

Two pointers / pair sum

Interactive explanation Gamified quiz, feedback & rewards

0 XP0 mastered
DSA enrichment · Learning goals & preparation

By the end, you can…

  • Explain Too small: increase the left value. Too large: decrease the right value.
  • Trace a small input and connect each operation to the algorithm’s rule.
  • Explain the implementation’s time and space cost and solve its mission.

Useful preparation: Reading arrays, indexing from zero and following step-by-step instructions. Suggested previous stop: Counting sort.

DSA uses suggested Foundation (Class 8), Builder (Class 9) and Advanced (Class 10) levels. It is an enrichment pathway.

Array patterns · Builder

Two pointers / pair sum

Ready. Step through the algorithm and explain each change.

  1. sort input; left = 0; right = n−1
  2. while left < right
  3. sum = a[left] + a[right]
  4. if sum == target: return pair
  5. move left if too small, else right

Up to 12 integers. Apply input to rebuild the trace and restart this topic’s quest.

A deliberate practice loop

Don’t just watch it move

  1. 1Before stepping, predict the next comparison, pointer move or state update.
  2. 2Read the explanation and identify the invariant that remains true.
  3. 3Change the input, then solve the concept quest without guessing.
About this pathway

From foundations to advanced patterns

The library covers core DSA techniques with bounded teaching examples. Foundation, Builder and Advanced describe learning progression, rather than a school-class syllabus. Snapshots are stored for playback and are excluded from algorithm-space labels.

Further study: MIT Introduction to Algorithms ↗