valid-triangle-number.py

# Time:  O(n^2)
# 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]
        :rtype: int
        """
        result = 0
        nums.sort()
        for i in xrange(len(nums)-2):
            if nums[i] == 0:
                continue
            k = i+2
            for j in xrange(i+1, len(nums)-1):
                while k < len(nums) and nums[i] + nums[j] > nums[k]:
                    k += 1
                result += k-j-1
        return result