611. Valid Triangle Number

Posted 2021-01-21 ordili

1. Question:

611. Valid Triangle Number

https://leetcode.com/problems/valid-triangle-number/

Given an array consists of non-negative integers, your task is to count the number of triplets chosen from the array that can make triangles if we take them as side lengths of a triangle.

Example 1:

Input: [2,2,3,4]
Output: 3
Explanation:
Valid combinations are: 
2,3,4 (using the first 2)
2,3,4 (using the second 2)
2,2,3

 

Note:

1. The length of the given array won‘t exceed 1000.
2. The integers in the given array are in the range of [0, 1000].

2. Solution:

import bisect


class Solution:
    def triangleNumber(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        if nums is None or len(nums) < 3:
            return 0
        size = len(nums)
        nums.sort()

        triangelNum = 0

        for i in range(0, size - 2):
            for j in range(i + 1, size - 1):
                max_third_value = nums[i] + nums[j]
                third_num_index = bisect.bisect_left(nums, max_third_value)
                if third_num_index > j:
                    triangelNum += third_num_index - j - 1

        return triangelNum