LeetCode: Is Subsequence

Given two strings, determine if one is a subsequence of the other

Posted on 19 Nov 2025 LeetCode Python

Difficulty: Easy

Solution

Create a pointer i for walking through s.

Walk through each character c in t. If c matches s[i], increment i by 1. If we have reached the end of s, then a subsequence is found.

Runtime

0 ms | Beats 100.00%

class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        if len(s) == 0:
            return True

        s_index = 0

        for c in t:
            if s[s_index] == c:
                s_index += 1
                if s_index >= len(s):
                    return True

        return False