countAndSay.go

/* https://leetcode.com/problems/count-and-say/#/description
The count-and-say sequence is the sequence of integers beginning as follows:
1, 11, 21, 1211, 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 nth sequence.

Note: The sequence of integers will be represented as a string.
note: 也就是输入n，输出第n个数，可以使用递归
*/

package lstring

import (
	"bytes"
	"strconv"
)

func countAndSay(n int) string {
	s := "1"
	for i := 1; i < n; i++ {
		ago, t := s[0], 1
		var r bytes.Buffer
		for j := 1; j < len(s); j++ {
			if ago == s[j] {
				t++
			} else {
				r.WriteString(strconv.Itoa(t))
				r.WriteByte(ago)
				t = 1
				ago = s[j]
			}
		}
		r.WriteString(strconv.Itoa(t))
		r.WriteByte(ago)
		s = r.String()
	}
	return s
}