The count-and-say sequence is a sequence of digit strings defined by the recursive formula:
countAndSay(1) = "1"countAndSay(n) is the way you would "say" the digit string from countAndSay(n-1), which is then converted into a different digit string.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.
方法：
递归即可
public String countAndSay(int n) { if( n <= 0) return ""; else if(n == 1) return "1"; String s = countAndSay(n - 1); StringBuilder ans = new StringBuilder(); StringBuilder same = new StringBuilder(); char pre = s.charAt(0); same.append(pre); for (int i = 1; i < s.length(); i++){ char c = s.charAt(i); if (c != pre){ int count = same.length(); ans.append(count); ans.append(pre); pre = c; same =new StringBuilder(); } same.append(c); } if (same.length()!=0){ int count = same.length(); ans.append(count); ans.append(pre); } return ans.toString(); }
参考链接：
https://leetcode.com/problems/count-and-say/
https://leetcode-cn.com/problems/count-and-say/
原文：https://www.cnblogs.com/diameter/p/14155212.html