# A happy number is a number that eventually reaches 1
# when repeatedly replaced by the sum of the squares of its digits.
#
# 19 = 1^2 + 9^2 = 82
# 19 -> 82 -> 68 -> 100 -> 1 eventually reaches 1
# 19 = happy number
# Compute the sum of squares of digits of n
def sumOfDigitSquares(n):
sum_ = 0
while n > 0:
d = n % 10
sum_ += d * d
n //= 10
return sum_
# Determine whether n is a happy number
def isHappy(n):
seen = set()
while n != 1 and n not in seen:
seen.add(n)
n = sumOfDigitSquares(n)
return n == 1
def main():
a, b = 1, 100
if a > b:
a, b = b, a
happyNumbers = []
for i in range(a, b + 1):
if isHappy(i):
happyNumbers.append(i)
print(f"Happy numbers in range [{a}, {b}]:")
for n in happyNumbers:
print(n, end=" ")
print()
if __name__ == "__main__":
main()
'''
run:
Happy numbers in range [1, 100]:
1 7 10 13 19 23 28 31 32 44 49 68 70 79 82 86 91 94 97 100
'''
