# Solving Leetcode Interviews in Seconds with AI: Repeated String Match


	# Introduction
	In this blog post, we will explore how to solve the LeetCode problem "686" using AI. LeetCode is a popular platform for preparing for coding interviews, and with the help of AI tools like [Chatmagic](https://www.chatmagic.app), we can generate solutions quickly and efficiently - helping you pass the interviews and get the job offer without having to study for months.

	# Problem Statement
	> Given two strings a and b, return the minimum number of times you should repeat string a so that string b is a substring of it. If it is impossible for b​​​​​​ to be a substring of a after repeating it, return -1. Notice: string "abc" repeated 0 times is "", repeated 1 time is "abc" and repeated 2 times is "abcabc".   Example 1:  Input: a = "abcd", b = "cdabcdab" Output: 3 Explanation: We return 3 because by repeating a three times "abcdabcdabcd", b is a substring of it.  Example 2:  Input: a = "a", b = "aa" Output: 2    Constraints:  1 <= a.length, b.length <= 104 a and b consist of lowercase English letters.  

	# Explanation
	Here's the breakdown of the solution:

*   **Determine the minimum repetitions:** Start by repeating string `a` a sufficient number of times to ensure the repeated string's length is at least the length of `b`.
*   **Substring Check:** Check if `b` is a substring of the repeated `a`. If found, return the number of repetitions.
*   **One More Repetition Check:** If `b` is not found, repeat `a` one more time and check again. This handles cases where `b` spans across the boundary of the initial repetitions. If still not found return -1.

*   **Runtime Complexity:** O(M * N) where M is the number of repetitions and N is the length of string `b`.
*   **Space Complexity:** O(M * K) where M is the number of repetitions and K is the length of string `a`.

	
	# Code
	```python
	def repeatedStringMatch(a: str, b: str) -> int:
    """
    Given two strings a and b, return the minimum number of times you should repeat string a
    so that string b is a substring of it. If it is impossible for b​​​​​​ to be a substring of a after
    repeating it, return -1.
    """
    n = len(a)
    m = len(b)
    repetitions = (m + n - 1) // n  # Minimum repetitions needed

    repeated_a = a * repetitions
    if b in repeated_a:
        return repetitions

    repeated_a += a
    if b in repeated_a:
        return repetitions + 1

    return -1
	```