How should I practice Str with Longest Len?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Microsoft online assessment problems in FastPrep.

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Problem · String

Str with Longest Len

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Problem statement

A prefix of a string S is any leading contiguous part of S. For example, the string "codility" has the following prefixes: "", "c", "co", "cod", "codi", "codil", "codili", "codilit", and "codility". A prefix of S is called proper if it is shorter 📏 than S.

A suffix of a string S is any trailing contiguous part of S. For example, the string "codility" has the following sufixes: "", "y", "ty", "ity", "lity", "ility", "dility", "odility" and "codility". A suffix of S is called proper if it is shorter than S.

Let's now write a func called strWithLongestLen(String S) in the editor 👉

Task of your func:

Find the len of the longest string that is both a proper suffix of S and a proper prefix of S.

: 𓏲🐋 ๋࣭ ࣪endless thanks, spike!˖✩࿐࿔ 🌊

🐳 Source note (Jul 17, 2026): The source asks for the length as an integer, but the online signature and example outputs used strings. They now return integers. The judged core task matches the visible source at about 99%.

Function

strWithLongestLen(S: String) → int

Examples

Example 1

S = "abbabba"return = 4

The string abba is both a proper prefix and a proper suffix of S. Its length is 4, and there is no longer valid string.

Example 2

S = "codility"return = 0

The only string that is both a proper prefix and a proper suffix is the empty string, whose length is 0.

Constraints

1 <= S.length() <= 1,000,000

String S consists only lower case english letters (a - z)