Solution: Permutation in String
Explore how to efficiently check if any permutation of a string appears as a contiguous substring within another string. Learn to use the sliding window technique to compare character counts, optimize the process for linear time complexity, and understand how to apply this pattern to solve related coding interview problems.
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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 ...