# 38. Count and Say

### Leetcode

<https://leetcode.com/problems/count-and-say/>

### 題目

The **count-and-say** sequence is a sequence of digit strings defined by the recursive formula:

* `countAndSay(1) = "1"`
* `countAndSay(n)` is the way you would "say" the digit string from `countAndSay(n-1)`, which is then converted into a different digit string.

To determine how you "say" a digit string, split it into the **minimal** number of groups so that each group is a contiguous section all of the **same character.** Then for each group, say the number of characters, then say the character. To convert the saying into a digit string, replace the counts with a number and concatenate every saying.

For example, the saying and conversion for digit string `"3322251"`:

![](https://assets.leetcode.com/uploads/2020/10/23/countandsay.jpg)

Given a positive integer `n`, return *the* `nth` *term of the **count-and-say** sequence*.

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

* **方法一**

遞迴計算

```
var countAndSay = function(n) {
    if(n===1) return '1';
    
    const str = countAndSay(n-1);
    let output = '';
    let count = 1;
    for(let i=0; i<str.length; i++) {
        if(str[i+1] === str[i]) count++;
        else {
            output += count.toString() + str[i];
            count = 1;
        }
    }
    
    return output;
};
```

Runtime: 72 ms, faster than 90.82% of JavaScript online submissions for Count and Say.

Memory Usage: 42 MB, less than 16.50% of JavaScript online submissions for Count and Say.

### 測資

```
console.log(countAndSay(5))
```

### 參考資料

<https://www.itread01.com/content/1546736419.html>
