Happy Number

202. Happy Number

Solution

1. Use set to remember the visited numbers.

   def isHappy(self, n):
    """
    :type n: int
    :rtype: bool
    """
    visited = set()
       
    while n not in visited:
        s = 0
        visited.add(n)
        while n != 0:
            s += (n % 10) ** 2
            n = n / 10
        if s == 1:
            return True
        n = s
    return False
   

   Solution - Floyd Cycle Detection

   Reference

2. If there is a cycle in the path, can stop to detection already. ```C int digitSquareSum(int n) { int sum = 0, tmp; while (n) { tmp = n % 10; sum += tmp * tmp; n /= 10; } return sum; }

bool isHappy(int n) { int slow, fast; slow = fast = n; do { slow = digitSquareSum(slow); fast = digitSquareSum(fast); fast = digitSquareSum(fast); } while(slow != fast); if (slow == 1) return 1; else return 0; } ```