{ "data": { "question": { "questionId": "38", "questionFrontendId": "38", "categoryTitle": "Algorithms", "boundTopicId": 978, "title": "Count and Say", "titleSlug": "count-and-say", "content": "

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

\n\n\n\n

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.

\n\n

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

\n\"\"\n

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

\n\n

 

\n

Example 1:

\n\n
\nInput: n = 1\nOutput: "1"\nExplanation: This is the base case.\n
\n\n

Example 2:

\n\n
\nInput: n = 4\nOutput: "1211"\nExplanation:\ncountAndSay(1) = "1"\ncountAndSay(2) = say "1" = one 1 = "11"\ncountAndSay(3) = say "11" = two 1's = "21"\ncountAndSay(4) = say "21" = one 2 + one 1 = "12" + "11" = "1211"\n
\n\n

 

\n

Constraints:

\n\n\n", "translatedTitle": "外观数列", "translatedContent": "

给定一个正整数 n ，输出外观数列的第 n 项。

\n\n

「外观数列」是一个整数序列，从数字 1 开始，序列中的每一项都是对前一项的描述。

\n\n

你可以将其视作是由递归公式定义的数字字符串序列：

\n\n\n\n

前五项如下：

\n\n
\n1.     1\n2.     11\n3.     21\n4.     1211\n5.     111221\n第一项是数字 1 \n描述前一项，这个数是 1 即 “ 一 个 1 ”，记作 \"11\"\n描述前一项，这个数是 11 即 “ 二 个 1 ” ，记作 \"21\"\n描述前一项，这个数是 21 即 “ 一 个 2 + 一 个 1 ” ，记作 \"1211\"\n描述前一项，这个数是 1211 即 “ 一 个 1 + 一 个 2 + 二 个 1 ” ，记作 \"111221\"\n
\n\n

要 描述 一个数字字符串，首先要将字符串分割为 最小 数量的组，每个组都由连续的最多 相同字符 组成。然后对于每个组，先描述字符的数量，然后描述字符，形成一个描述组。要将描述转换为数字字符串，先将每组中的字符数量用数字替换，再将所有描述组连接起来。

\n\n

例如，数字字符串 \"3322251\" 的描述如下图：

\n\"\"\n\n\n

 

\n\n

示例 1：

\n\n
\n输入：n = 1\n输出：\"1\"\n解释：这是一个基本样例。\n
\n\n

示例 2：

\n\n
\n输入：n = 4\n输出：\"1211\"\n解释：\ncountAndSay(1) = \"1\"\ncountAndSay(2) = 读 \"1\" = 一 个 1 = \"11\"\ncountAndSay(3) = 读 \"11\" = 二 个 1 = \"21\"\ncountAndSay(4) = 读 \"21\" = 一 个 2 + 一 个 1 = \"12\" + \"11\" = \"1211\"\n
\n\n

 

\n\n

提示：

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