Two Pointers & Sliding Window Visualizers

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Step through every Two Pointers & Sliding Window problem with animated runtime state, source highlighting, and curated test cases. Built for coding-interview prep and durable algorithmic intuition.

Sort first, then lock one anchor and solve the remaining pair with inward pointers.

Sorted Two Pointers

Container With Most Water

Measure area with both outer walls, then move the shorter wall inward to search for a taller boundary.

Greedy Two Pointers

Find the Index of the First Occurrence in a String

Slide a short matching window across the haystack and compare the candidate substring.

Advance the source string only when characters match; the target string keeps moving regardless.

Forward Two Pointers

Longest Repeating Character Replacement

Keep the window as large as possible while at most k characters differ from the most frequent letter inside it.

Sliding Window + Frequency Count

Longest Substring Without Repeating Characters

Expand the right edge, and whenever a duplicate appears, shrink the left edge until the window is valid again.

Sliding Window + Set

Permutation in String

Slide a fixed-size window and compare frequency balance with the target permutation.

Fixed Window Frequency Match

Sliding Window Maximum

Maintain a decreasing deque of indices so the current maximum is always at the front.

Sliding Window + Monotonic Deque

Trapping Rain Water

Track the best wall seen from both sides and trap water above shorter boundaries.

Two Pointers with Running Max

Scan once with a hashmap of seen values and resolve the complement the moment it appears.

Hash Map + Pair Scan

Two Sum II - Input Array Is Sorted

Use the sorted order to squeeze two pointers inward until the sum matches the target.

Opposing Two Pointers