# 392. Is Subsequence

### Leetcode

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

### 題目

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
```

### 解答 <a href="#ti-jie" id="ti-jie"></a>

* **方法一**

```
var isSubsequence = function(s, t) {
    let indexS = 0;
    let indexT = 0;
    while(indexS < s.length) {
        const char = s[indexS];
        const newIndex = t.indexOf(char, indexT);
        if(newIndex === -1) return false;
        // 從 t 的下個 index 開始找有沒有符合的 char
        indexT = newIndex + 1;
        indexS++;
    }
    return true;
};
```

Runtime: 64 ms, faster than 98.32% of JavaScript online submissions for Is Subsequence.

Memory Usage: 38.6 MB, less than 83.95% of JavaScript online submissions for Is Subsequence.

### 測資

```
let s = "abc", t = "ahbgdc"; // true
// s = "axc", t = "ahbgdc"; // false
// s = "aaaaaa", t="bbaaaa"; // false

console.log(isSubsequence(s, t))
```
