## Description

https://leetcode.com/problems/is-subsequence/

Given two strings `s`

and `t`

, check if `s`

is a **subsequence** of `t`

.

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.

**Follow up:** If there are lots of incoming `s`

, say `s`

where _{1}, s_{2}, ..., s_{k}`k >= 10`

, and you want to check one by one to see if ^{9}`t`

has its subsequence. In this scenario, how would you change your code?

## Explanation

Check if iterating the t string can find all s string in sequence.

## Python Solution

```
class Solution:
def isSubsequence(self, s: str, t: str) -> bool:
if not s:
return True
i = 0
for c in t:
if c == s[i]:
i += 1
if i >= len(s):
break
if i == len(s):
return True
return False
```

- Time Complexity: O(N).
- Space Complexity: O(1).