Operation counts, brute force vs window / two pointers (counted, not timed)
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Max sum of k=100 consecutive elements: element reads
       n    brute force sliding window    ratio
    1000         90,100          1,900    47.4x
    2000        190,100          3,900    48.7x
    4000        390,100          7,900    49.4x
    8000        790,100         15,900    49.7x

Pair search, target absent (worst case) in a sorted array 0..n-1: checks / steps
       n      all pairs   two pointers
    1000        499,500            999
    2000      1,999,000          1,999
    4000      7,998,000          3,999
    8000     31,996,000          7,999

minWindow on random strings over A-D, t="ABCD" (seed 42): pointer moves
The loop is nested but each pointer only moves forward, so total moves stay linear.
       n  right moves  left moves  valid windows
    1000        1,000         996            996
    2000        2,000       1,996          1,996
    4000        4,000       3,996          3,996
    8000        8,000       7,993          7,993