Leetcode 2272. Substring With Largest Variance

Find the maximum possible difference between counts of any two lowercase letters over all contiguous substrings of s — i.e., the largest (count(a) - count(b)) achievable in any substring. Key idea/pattern: treat each ordered pair of distinct letters and run a Kadane-like linear scan to maximize the difference while ensuring both letters appear in the substring (|s| up to 10^4).