[LeetCode/LintCode] Happy Number

崔晓明发布于2019-08-14 15:11 / 1968人阅读

Problem

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
1^2 + 9^2 = 82
8^2 + 2^2 = 68
6^2 + 8^2 = 100
1^2 + 0^2 + 0^2 = 1

Solution updated 2018-9

class Solution {
    public boolean isHappy(int n) {
        Set record = new HashSet<>();
        while (n != 1) {
            if (record.contains(n)) return false;
            record.add(n);
            int sum = 0;
            while (n != 0) {
                //calculate sum
                sum += Math.pow(n%10, 2);
                n /= 10;
            }
            n = sum;
        }
        return true;
    }
}

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