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Number of Substrings Containing All Three Characters [Medium]
Count substrings containing at least one a, b, and c using the last-seen indices shortcut for O(n) time.
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Subarray Sum Divisible by K [Medium] — Prefix Sum Modulo
Count subarrays with sum divisible by k using prefix sum modulo k and a frequency map of remainders.
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Find K Closest Elements [Medium] — Binary Search + Two Ptr
Find k closest integers to x in a sorted array using binary search to locate the optimal left boundary of the window.
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Count Subarrays With Fixed Bounds [Hard] — One-Pass Window
Count subarrays where min=minK and max=maxK using a single pass tracking the last invalid position and last positions of minK and maxK.
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Max Consecutive Ones [Medium] — K-Flip Sliding Window
Find the maximum consecutive ones in a binary array when you can flip at most k zeros, identical to the Max Consecutive Ones III pattern.
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