Repeated Substring Pattern

Problem

Given a string pattern, check if the string can be formed by taking a substring of it and repeating it multiple times. Return true if such a pattern exists, otherwise return false.

Examples

isRepeatingPattern("zyzy")
// returns true
// It's the pattern "zy" repeated twice.

isRepeatingPattern("xyx")
// returns false

isRepeatingPattern("mnmnmn")
// returns true
// It's the pattern "mn" repeated three times.