message: Update valid-triangle-number.py
diff: # Space: O(1)
  class Solution(object):
  + def triangleNumber(self, nums):
  + """
  + :type nums: List[int]
  + :rtype: int
  + """
  + result = 0
  + nums.sort()
  + for i in reversed(xrange(2, len(nums))):
  + left, right = 0, i-1
  + while left < right:
  + if nums[left]+nums[right] > nums[i]:
  + result += right-left
  + right -= 1
  + else:
  + left += 1
  + return result
  +
  +
  +# Time: O(n^2)
  +# Space: O(1)
  +class Solution2(object):
  def triangleNumber(self, nums):
  """
  :type nums: List[int]
  