{ "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 substrings such that each substring contains exactly one unique digit. Then for each substring, say the number of digits, then say the digit. Finally, concatenate every said digit.

\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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