3sum smaller

class Solution:
    def twoSumSmaller(self, nums, start, target):
        lo = start
        hi = len(nums) - 1
        count = 0
        while lo < hi:
            if nums[lo] + nums[hi] < target:
                count += hi - lo
                lo += 1
            else:
                hi -= 1
        return count

    def threeSumSmaller(self, nums: List[int], target: int) -> int:
        if len(nums) < 3:
            return 0
        nums.sort()
        res = 0
        for i in range(len(nums) - 2):
            res += self.twoSumSmaller(nums, i + 1, target - nums[i])

        return res

3Sum Smaller

---

Given an array of n integers nums and an integer target, find the number of index triplets i, j, k with 0 <= i < j < k < n that satisfy the condition nums[i] + nums[j] + nums[k] < target.

 

Example 1:

Input: nums = [-2,0,1,3], target = 2
Output: 2
Explanation: Because there are two triplets which sums are less than 2:
[-2,0,1]
[-2,0,3]

Example 2:

Input: nums = [], target = 0
Output: 0

Example 3:

Input: nums = [0], target = 0
Output: 0

 

Constraints:

• n == nums.length
• 0 <= n <= 3500
• -100 <= nums[i] <= 100
• -100 <= target <= 100