input: Write a python function to check if a given number is a perfect square.
  assert issquare(25) == True
  assert issquare(12) == False
  assert issquare(0) == True
  assert issquare(1) == True
  assert issquare(49) == True
output: def issquare(n):
      if n < 0:
          return False
      root = int(n**0.5)
      return root * root == n