In this article, we are going to learn to find Happy Number using Java. Let’s first understand, what is Happy Number?
Table of Contents
What is a Happy Number?
A number which leaves 1 as a result after a sequence of steps and in each step number is replaced by the sum of squares of its digit. For example, if we check whether 23 is a Happy Number, then sequence of steps are
Step 1: 2×2+3×3 = 4+9 = 13 // Sum of square of each digit
Step 2: 1×1+3×3 = 1+9 = 10
Step 3: 1×1+0x0 = 1 (A Happy Number)
We will see two approaches to find happy number in java.
Using Hashset
In this approach, we will use Hashset to tract the cycle and if sum=1 at the end of the cycle, then it is happy number.
Algorithm
- Take one variable
sumfor storing sum of square. - Intialize a HashSet
numbers, we will use this HashSet to track repeating cycle. - Iteate through while loop until we get same number again and do following:
- Calculate the square of each digit present in the number and add it to the variable
sumand divide thenumberby 10. - Assign
sumtonumberafter each iteration
- Calculate the square of each digit present in the number and add it to the variable
- If result
sumis equal to 1, then the number is aHappy Number. - Else the number is not happy Number.
Note: A number can not be a Happy Number if it makes a loop in its sequence. For example,
Example
Here is complete example to find Happy number in java.
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import java.util.HashSet; import java.util.Set; public class Main { public static void main(String args[]) { int number = 1111111; int sum = 0; Set<Integer> numbers = new HashSet<Integer>(); while(numbers.add(number)){ sum = 0; while(number>0) { sum += (number % 10)*(number % 10); number /=10; } number = sum; } // if sum = 1, it is happy number if(sum == 1) { System.out.println("It is a happy number"); }else { System.out.println("It is not a happy number"); } } } |
Output
Using slow and fast pointers
In this approach, we will use slow and fast pointer to track the cycle.
Algorithm
- initialize two variables
slowandfastwith given number. - Iterate through do while loop until we get a cycle (
slow!=fast)- Move
slowpointer once by callinggetSumOfSquareOfDigit()once. - Move
fastpointer twice by callinggetSumOfSquareOfDigit()twice.
- Move
- If
slowis equal to 1 at the end of cycle, it means it ishappy number.
Example
Here is complete example to find Happy number in java.
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package org.arpit.java2blog; public class HappyNumberSlowFast { static int getSumOfSquareOfDigit(int num) { int ss = 0; while (num != 0) { ss += (num % 10) * (num % 10); num /= 10; } return ss; } // method return true if n is Happy number static boolean isHappynumber(int num) { int slow, fast; // initialize slow and fast by num slow = fast = num; do { // move slow number by one step slow = getSumOfSquareOfDigit(slow); // move fast number by two steps fast = getSumOfSquareOfDigit(getSumOfSquareOfDigit(fast)); } while (slow != fast); // If slow and fast point meet and slow is equals to 1, // then it is happy number return (slow == 1); } // Main method public static void main(String[] args) { int n = 1111111; if (isHappynumber(n)) System.out.println(n + " is a Happy number"); else System.out.println(n + " is not a Happy number"); } } |
Output
That’s all about How to find Happy Number in Java
