Solution: Permutation in String
Explore how to check if any permutation of a string appears as a contiguous substring within another by using the sliding window technique. Understand character frequency matching and practice an efficient approach that runs in linear time with constant space usage.
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Statement
Given two strings, s1 and s2, determine whether any permutation of s1 appears as a contiguous substring within s2. In other words, return TRUE if s2 contains a substring that uses the same characters as s1, with the same frequencies, but possibly in a different order. Otherwise, FALSE.
A permutation of a string is any possible arrangement of all its characters. For example, for the string “ab”, the permutations are: “ab” and “ba”.
Constraints:
s1.length, s2.lengths1ands2consist of lowercase English letters.
Solution
A naive approach would be to generate all possible rearrangements of s1 and check whether any appear in s2. But that would quickly become inefficient for longer strings, because the number of permutations grows extremely fast. For a three-letter string like "abc", there are ...