LeetCode link: 459. Repeated Substring Pattern, difficulty: Easy.

Given a string s, check if it can be constructed by taking a substring of it and appending multiple copies of the substring together.

Input: s = "abcabcabcabc"

Output: true

Explanation: It is the substring "abc" four times or the substring "abcabc" twice.

Input: s = "aba"

Output: false

• 1 <= s.length <= 10000
• s consists of lowercase English letters.

The key to solving this problem is to see clearly that if s can be obtained by repeating the substring, then the starting letter of the substring must be s[0]. Once you understand this, the scope of substring investigation is greatly narrowed.

• Time: O(N * N).
• Space: O(N).

class Solution:
    def repeatedSubstringPattern(self, s: str) -> bool:
        for i in range(1, int(len(s) / 2) + 1):
            if len(s) % i == 0 and s[:i] * int(len(s) / i) == s:
                return True

        return False

// Welcome to create a PR to complete the code of this language, thanks!

var repeatedSubstringPattern = function (s) {
  for (let i = 1; i <= s.length / 2; i++) {
    if (s.length % i != 0) {
      continue
    }

    if (s.slice(0, i).repeat(s.length / i) == s) {
      return true
    }
  }

  return false
};

// Welcome to create a PR to complete the code of this language, thanks!

// Welcome to create a PR to complete the code of this language, thanks!

// Welcome to create a PR to complete the code of this language, thanks!

# Welcome to create a PR to complete the code of this language, thanks!

// Welcome to create a PR to complete the code of this language, thanks!