Count and Say

依然觉得蛮无聊的，注意返回的是第n个（从1开始算起）string

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.

比如n=4, return 1211

 

public class Solution {
    public String countAndSay(int n) {
        if(n<1) return "";
        String s="1";
        int cnt=1;
        
        for(int i=0;i<n-1;i++){
            StringBuilder t = new StringBuilder();
            for(int j=0;j<s.length();j++){
                if(j<s.length()-1 && s.charAt(j)==s.charAt(j+1)){
                    cnt++;
                }else{
                    t.append(cnt+""+s.charAt(j));
                    cnt=1;
                }
            }
            s =t.toString();
        }
        return s;
    }
}