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 in base-ten, and repeat the process until the number either equals 1 (where it will stay), or it loops endlessly in a cycle that does not include 1. Those numbers for which this process ends in 1 are happy numbers, while those that do not end in 1 are unhappy numbers (or sad numbers)[1].
package education.jtrainer.ishappy; public class IsHappy { static int iteration=0; static private Boolean isHappy(String a){ iteration++; System.out.println("iteration n."+iteration+" input value:"+a); int value=0; int size=a.length(); int sum=0; for (int i=0;i<size;i++) { char element=a.charAt(i); int valueInt=Character.getNumericValue(element); sum=sum+valueInt*valueInt; } if (sum==1) return true; else { if (isUnHappy(sum)) return false; return(isHappy(Integer.toString(sum))); } } static private Boolean isUnHappy(int b){ Integer[] unhappylist = new Integer[]{4, 16, 37, 58, 89, 145, 42, 20}; for (int i=0;i<8;i++){ if (b==unhappylist[i]){ return true; } } return false; } public static void main(String[] args) { if (isHappy("49").equals(Boolean.TRUE)){ System.out.println("number is happy"); } else { System.out.println("number is unhappy"); } } }
Download from github:
https://github.com/jtrainer-education/HappyJava
References
[1] – https://en.wikipedia.org/wiki/Happy_number#cite_note-1