Leetcode trick: finding a prefix and a suffix is the dual problem of finding the subarray between them.

Some LeetCode questions say: "find a prefix and a suffix with some property and with maximum combined length."

However, it's hard to consider all possible prefix-suffix combinations.

But what is between a prefix and a suffix? A subarray!

Such questions can often be rephrased in terms of finding the *smallest* subarray with some complementary property.

And you can use a sliding window for that.