Check If String Is a Prefix of Array — LeetCode 1961 Python Solution

The problem

Given a string s and an array of strings words, determine whether s is a prefix string of words. A string s is a prefix string of words if s can be made by concatenating the first k strings in words for some positive k no larger than words.length.

Example

Input

s = "iloveleetcode", words = ["i","love","leetcode","apples"]

Output

true

Explanation

s can be made by concatenating "i", "love", and "leetcode" together.

Python solution

class Solution:
    def isPrefixString(self, s: str, words: List[str]) -> bool:
        n, m = len(s), 0
        for i, w in enumerate(words):
            m += len(w)
            if m == n:
                return "".join(words[: i + 1]) == s
        return False

Complexity

Pattern: Two Pointers

Use the order already in the input to discard half the search space at every step. LeetCode 1961. Check If String Is a Prefix of Array is filed here on both counts: the reference solution below belongs to the algorithm family this hub collects, and LeetCode tags it Two Pointers.

The two pointers guide has the Python template for the pattern and the 201 LeetCode problems that use it.

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