Leetcode: 3Sum Smaller

3Sum Smaller



Similar Problems:


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
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