LeetCode 76 Minimum Window Substring - Why Naive Fails

Try all substrings of s. For each, check if it contains all characters of t.

There are $O(n^2)$ substrings. Checking each against t takes $O(m)$ comparisons. Total: $O(n^2 \cdot m)$.

For $n = m = 10^5$, that's $10^{15}$ operations. Far too slow.