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g0001_0100.s0038_count_and_say.readme.md Maven / Gradle / Ivy

38\. Count and Say

Medium

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_.

**Example 1:**

**Input:** n = 1

**Output:** "1"

**Explanation:** This is the base case. 

**Example 2:**

**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" 

**Constraints:**

*   `1 <= n <= 30`