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. 快乐数的具体解释参考这里
由上文的资料可得，不是快乐数的数称为不快乐数（unhappy number），所有不快乐数的数位平方和计算，最後都会进入 4 → 16 → 37 → 58 → 89 → 145 → 42 → 20 → 4 的循环中。 那么，可以用hashset保存这些值，遇到直接返回false即可。
public boolean isHappy(int n) { if (n == 0) return false; if (n == 1) return true; int sum = 0; HashSet<Integer> set = new HashSet<>(); set.add(4); set.add(16); set.add(37); set.add(58); set.add(89); set.add(145); set.add(42); set.add(20); while (n != 0) { sum += (n % 10) * (n % 10); n /= 10; } return !set.contains(sum) && isHappy(sum); }新闻热点
疑难解答
