刚刚笔试遇到的。好像很简单，但又不容易写的
611 有效三角形

    def triangleNumber(self, nums):
        count = 0
        nums.sort()
        for i in range(len(nums) - 2):
            k = i + 2
            for j in range(i + 1, len(nums) - 1):
                if nums[i] == 0:
                    break
                while k < len(nums) and nums[i] + nums[j] > nums[k]:
                    k += 1
                count += k - j - 1
        return count