38. Count and Say

The count-and-say sequence is the sequence of integers with the first five terms as following:1. 12. 113. 214. 12115. 1112211 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 where 1 ≤ n ≤ 30, generate the nth term of the count-and-say sequence.Note: Each term of the sequence of integers will be represented as a string.Example 1:Input: 1Output: “1"Example 2:Input: 4Output: “1211"难度：easy题目：count-and-say 序列如下如示：1. 12. 113. 214. 12115. 1112211 读作1个1或1111 读作2个1或2121 读作1个2，接着1个1 或1211给定一个整数n 大于等于1小于等于30, 产生第n组序列。注意：每项由整数组成的序列以字符串表示。Runtime: 3 ms, faster than 72.13% of Java online submissions for Count and Say.Memory Usage: 25.8 MB, less than 98.33% of Java online submissions for Count and Say.class Solution { public String countAndSay(int n) { String str = “”; for (int i = 0; i < n; i++) { str = generateNext(str); } return str; } private String generateNext(String s) { if (s.isEmpty()) { return “1”; } // add and end flag s += “.”; int counter = 1; StringBuilder str = new StringBuilder(); for (int i = 1; i < s.length(); i++) { if (s.charAt(i) != s.charAt(i - 1)) { str.append(counter).append(s.charAt(i - 1)); counter = 1; } else { counter++; } } return str.toString(); }}