Happy Number I - Floyds cycle detection
Write an algorithm to determine if a number n 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.
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.
Return true if n is a happy number, and false if not.
import java.util.LinkedList;
class Solution {
public boolean isHappy(int n) {
int slow = n;
int fast = n;
//while loop is not used here because initially slow and
//fast pointer will be equal only, so the loop won't run.
do {
//slow moving one step ahead and fast moving two steps ahead
slow = square(slow);
fast = square(square(fast));
} while (slow != fast);
//if a cycle exists, then the number is not a happy number
//and slow will have a value other than 1
return slow == 1;
}
//Finding the square of the digits of a number
public int square(int num) {
int ans = 0;
while(num > 0) {
int remainder = num % 10;
ans += remainder * remainder;
num /= 10;
}
return ans;
}
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