题解 | 快乐数

import java.util.*;

public class Solution {
    public int powSum(int n){
        int ans = 0;
        while(n>0){
            int t = n%10;
            ans += t*t;
            n/=10;
        }
        return ans;
    }
    public boolean happynum (int n) {
       //一般来说数位的平方和，会比原来的数小
       //有限的范围计算无数次，必然出现重复的数
      Set<Integer> set = new HashSet<>();
      int cur = powSum(n);
      while(cur!=1&&!set.contains(cur)){
        set.add(cur);
        cur = powSum(cur);
      }
      if(cur==1)return true;
      else return false;
    }
}