Repeated String Match — LeetCode 686 Python Solution

The problem

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.

Example

Input

a = "abcd", b = "cdabcdab"

Output

3

Explanation

We return 3 because by repeating a three times "abcdabcdabcd", b is a substring of it.

Python solution

class Solution:
    def repeatedStringMatch(self, a: str, b: str) -> int:
        m, n = len(a), len(b)
        ans = ceil(n / m)
        t = [a] * ans
        for _ in range(3):
            if b in ''.join(t):
                return ans
            ans += 1
            t.append(a)
        return -1

Complexity

Pattern: Hash Map

Trade memory for time: remember what you have seen so the second pass never happens. LeetCode 686. Repeated String Match is filed here because the reference solution below belongs to the algorithm family this hub collects, even though its LeetCode tags point elsewhere.

The hash map guide has the Python template for the pattern and the 709 LeetCode problems that use it.

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