202. Happy Number
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:
Input: 19 Output: true Explanation: 12 + 92 = 82 82 + 22 = 68 62 + 82 = 100 12 + 02 + 02 = 1
package leetcode.easy; public class HappyNumber { public boolean isHappy(int n) { if (n == 0) { return false; } while (n != 1) { int n2 = n; n = 0; while (n2 > 0) { n += (n2 % 10) * (n2 % 10); n2 /= 10; } if (n == 4) { return false; } } return true; } @org.junit.Test public void test() { System.out.println(isHappy(19)); } }