mediumDSA

What is the two-pointer technique?

Q: What is the two-pointer technique?

**Intuition.** Instead of a nested loop checking every pair (O(n²)), you move **two indices** through the data intelligently — often from both ends inward — so each element is visited once. That collapses many pair/subarray problems to **O(n)**. sorted array, find a pair summing to 18 <rect x="140" y="50"

192 views

Understand the problem

Explain two pointers.

two-pointers

Attempt it yourself

Sketch your approach before reading the solution — that's what interviews test.

Stuck? AI Nudge Available

Get a conceptual hint to guide your logic without spoiling the final implementation.

Study the solution

The solution is waiting

Give it an honest attempt first — then compare your thinking with the full walkthrough.

Read the code

Pair sum in a sorted array

Run Playground

def pair_sum(arr, target):
    left, right = 0, len(arr) - 1
    while left < right:
        s = arr[left] + arr[right]
        if s == target:
            return (left, right)
        if s < target:
            left += 1
        else:
            right -= 1
    return None


# --- demo ---
print(pair_sum([2, 7, 8, 11, 15, 18], 18))   # (1, 3)  -> 7 + 11

Join the discussion

Discussion (0)

No responses yet. Be the first to share what you think.

What is the sliding window technique?

How do you build a binary tree from preorder and inorder traversals?