> For the complete documentation index, see [llms.txt](https://yingzehou.gitbook.io/docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://yingzehou.gitbook.io/docs/leetcode/string/count-and-say.md).

# Count and Say

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*.

```
Input: n = 4
Output: "1211"
Explanation:
countAndSay(1) = "1"
countAndSay(2) = say "1" = one 1 = "11"
countAndSay(3) = say "11" = two 1's = "21"
countAndSay(4) = say "21" = one 2 + one 1 = "12" + "11" = "1211"
```

## Idea

{% hint style="info" %}
Recursion
{% endhint %}

If n=1, base case, return "1"

If not, recursively call the method; When get a intermediate string, like "21", get the count of each element in sequence and connect count+number together to form the result

## Code

```java
public String countAndSay(int n) {
        if(n == 1){
            return "1";
        }
        String curr = countAndSay(n-1);
        int currInd = 1;
        String base = curr.substring(0,1);
        int count = 1;
        String result = "";
        if(curr.length()==1){
            return "1"+base;
        }
        while(currInd<curr.length()){
            if(curr.substring(currInd, currInd+1).equals(base)){
                count++;
            }
            else{
                result += String.valueOf(count)+base;
                base = curr.substring(currInd, currInd+1);
                count=1;
            }
            currInd++;
        }
        result+=String.valueOf(count)+base;
        return result;
    }
```


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