We use a hash set to detect cycles. If we encounter a sum that we've seen before and it's not 1, the number will never reach 1.

1. Initialize seen = set().
2. While n != 1 and n not in seen:
   • seen.add(n).
   • Calculate sum of squares of digits of n.
   • Update n with this sum.
3. Return n == 1.

• Time Complexity: O(log N) (finding digits and summing squares).
• Space Complexity: O(log N) (to store seen numbers).

def is_happy(n):
    seen = set()
    while n != 1 and n not in seen:
        seen.add(n)
        n = sum(int(digit) ** 2 for digit in str(n))
    return n == 1