LeetCode——Happy Number

Description：

Write an algorithm to determine if a number is "happy".

A happy number is a number defined by the following process: Starting with any positive integer, replace the number by the sum of the squares of its digits, and repeat the process until the number equals 1 (where it will stay), or it loops endlessly in a cycle which does not include 1. Those numbers for which this process ends in 1 are happy numbers.

Example: 19 is a happy number

• 1² + 9² = 82
• 8² + 2² = 68
• 6² + 8² = 100
• 1² + 0² + 0² = 1

public class Solution {
    public boolean isHappy(int n) {
        ArrayList<String> tList = new ArrayList<>();
        String sn = new String(n+"");
        while(true) {
            String t = calcu(sn);
            if(t.equals("1")) {
                return true;
            }
            if(tList.contains(t)) {
                return false;
            }
            tList.add(t);
            sn = t;
        }
        
    }
    public static String calcu(String str) {
        int t = 0;
        for(int i=0; i<str.length(); i++) {
            t += Integer.parseInt(str.charAt(i)+"") * Integer.parseInt(str.charAt(i)+"");
        }
        return new String(t+"");
    }
}