## 1. Problem

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
```

Constraints:

- 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
```