7646: [CSES Problem Set] Repeating Substring
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Description
A repeating substring is a substring that occurs in two (or more) locations in the string. Your task is to find the longest repeating substring in a given string.
Input
The only input line has a string of length $n$ that consists of characters a–z.
Output
Print the longest repeating substring. If there are several possibilities, you can print any of them. If there is no repeating substring, print $-1$.
Constraints
$1≤n≤10^5$
Sample 1 Input
cabababc
Sample 1 Output
abab