[leetcode] 392. Is Subsequence _ Algorithm Problem Solve for python

1. Problem

392. Is Subsequence

Given two strings s and t, return true if s is a subsequence of t, or false otherwise.

A subsequence of a string is a new string that is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (i.e., “ace” is a subsequence of “abcde” while “aec” is not).

Example 1:

Input: s = "abc", t = "ahbgdc"
Output: true

Example 2:

Input: s = "axc", t = "ahbgdc"
Output: false


  • 0 <= s.length <= 100
  • 0 <= t.length <= 10^4
  • s and t consist only of lowercase English letters.

2. Solution

I solved this problem like this.

  • Complexity
    • Time complexity : O(N)
    • Space complexity : O(1)
  • Step
    • if s len is 0, return True
    • confirm s text(using s_idx) in t while for statement.
class Solution:
    def isSubsequence(self, s: str, t: str) -> bool:
        if not len(s):
            return True
        s_idx = 0
        for _t in t:
            if s[s_idx] == _t:
                s_idx += 1
            if s_idx >= len(s):
                return True

        return False