3Sum Smaller

Similar Problems:

- Series: TwoSum Problems & Follow-Up
- 3Sum Closest
- CheatSheet: Leetcode For Code Interview
- Tag: #twosum, #3sum

Given an array of n integers nums and a 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.

For example, given nums = [-2, 0, 1, 3], and target = 2.

Return 2. Because there are two triplets which sums are less than 2:

[-2, 0, 1] [-2, 0, 3]

Follow up:

Could you solve it in O(n^2) runtime?

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

## Blog link: https://code.dennyzhang.com/3sum-smaller ## Basic Ideas: two pointer ## Complexity: Time O(n*n), Space O(1) class Solution: def threeSumSmaller(self, nums, target): """ :type nums: List[int] :type target: int :rtype: int """ nums.sort() length = len(nums) res = 0 for i in range(0, length-2): l, r = i+1, length-1 while l<r: v = nums[i]+nums[l]+nums[r] if v < target: res += (r-l) l += 1 else: r -= 1 return res