有效三角形个数

class Solution:
    def triangleNumber(self, nums: List[int]) -> int:
        # 对数组排序
        nums.sort()
        ans = 0
        for i in range(len(nums)-2):
            for j in range(i+1, len(nums)-1):
                left = j + 1
                right = len(nums) - 1 
                while left <= right:
                    mid = (left + right) // 2
                    if nums[i] + nums[j] > nums[mid]:
                        left = mid + 1
                    else:
                        right = mid - 1

                ans = ans + (left - j - 1)
        return ans