intermediate
10 min read
Longest Substring Without Repeating Characters
A repeated character is not a reason to restart the scan. It is a reason to move the left boundary to the first position that makes the current window…
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Sliding Window
Maintain a valid moving window while expanding and shrinking to optimize contiguous subarray and substring problems.
Problems
Problems in Sliding Window
Practice problems that share this primary solution pattern and compare the clues that reveal it.
expert
13 min read
Substring with Concatenation of All Words
Equal-width tokens turn a permutation problem into a finite set of aligned frequency windows.
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advanced
13 min read
Minimum Window Substring
The hard part is not moving two pointers. It is preserving the target’s multiplicity while the window changes.
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