> ## Documentation Index
> Fetch the complete documentation index at: https://leetcode-py.wisl.dev/llms.txt
> Use this file to discover all available pages before exploring further.

> ## Agent Instructions
> leetcode-py is a Python LeetCode practice environment generator with one CLI: lcpy. It is not a service or platform.
> Each problem is a directory under leetcode/ with README.md, solution.py, test_solution.py, helpers.py, and playground.ipynb. lcpy gen creates them from JSON templates bundled with the package.
> Examples are backed by tests; copy them verbatim.

# Is Subsequence Python Solution with Tests

> Tested Python solution for LeetCode 392 with 13 pytest cases. Generate a practice environment with lcpy.

LeetCode 392, Easy. Topics: Two Pointers, String, Dynamic Programming. [View on LeetCode](https://leetcode.com/problems/is-subsequence/description/).

Generate this problem as a practice environment: tested reference solution, 13 [parametrized pytest cases](/practice/testing), and a playground notebook:

```bash theme={"theme":{"light":"github-light","dark":"github-dark"}}
lcpy gen -n 392   # by problem number
lcpy gen -s is_subsequence   # by problem name
```

## 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).

### Examples

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

```
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:** Suppose there are lots of incoming `s`, say `s1, s2, ..., sk` where `k >= 10^9`, and you want to check one by one to see if `t` has its subsequence. In this scenario, how would you change your code?

## Solution

Reference implementation from [solution.py on GitHub](https://github.com/wislertt/leetcode-py/blob/main/leetcode/is_subsequence/solution.py), full suite in [test\_solution.py](https://github.com/wislertt/leetcode-py/blob/main/leetcode/is_subsequence/test_solution.py):

```python theme={"theme":{"light":"github-light","dark":"github-dark"}}
class Solution:
    # Time: O(len(t))
    # Space: O(1)
    def is_subsequence(self, s: str, t: str) -> bool:
        i = 0
        for char in t:
            if i < len(s) and char == s[i]:
                i += 1
        return i == len(s)
```

## Complexity

| Time      | Space |
| --------- | ----- |
| O(len(t)) | O(1)  |

## Tags

[NeetCode All](/catalog/neetcode), [AlgoMaster 75](/catalog/algo-master-75).