38. Count and Say

Problem

The count-and-say sequence is the sequence of integers with the first five terms as following:

1.     1
2.     11
3.     21
4.     1211
5.     111221

1 is read off as "one 1" or 11. 11 is read off as "two 1s" or 21. 21 is read off as "one 2, then one 1" or 1211. Given an integer n, generate the n^{th} term of the count-and-say sequence.

Note: Each term of the sequence of integers will be represented as a string.

Example 1:

Input: 1
Output: "1"

Example 2:

Input: 4
Output: "1211"

Related Topics:

String

Analysis

遍历并统计数字。

Code

class Solution {

    fun countAndSay(n: Int): String {

        var string = "1"
        var stringBuilder: StringBuilder
        var count: Int

        (2..n).forEach {

            stringBuilder = StringBuilder()
            count = 1

            (0 until string.length - 1).forEach {
                when {
                    string[it] == string[it + 1] -> count++
                    else -> {
                        stringBuilder.append(count).append(string[it])
                        count = 1
                    }
                }
            }
            stringBuilder.append(count).append(string.last())

            string = stringBuilder.toString()
        }

        return string
    }
}