3 Sum closest [Two Pointers]

Time: O(N^2); Space: O(1); medium

Given an array nums of N integers, find three integers in nums such that the sum is closest to a given number, target. Return the sum of the three integers. You may assume that each input would have exactly one solution.

Example 1:

Input: nums = [-1 2 1 -4], target = 1

Output: 2

Explanation:

• -1 + 2 + 1 = 2

class Solution1(object):
    def threeSumClosest(self, nums, target):
        """
        :type nums: List[int]
        :type target: int
        :rtype: int
        """
        nums, result, min_diff, i = sorted(nums), float("inf"), float("inf"), 0
        while i < len(nums) - 2:
            if i == 0 or nums[i] != nums[i - 1]:
                j, k = i + 1, len(nums) - 1
                while j < k:
                    diff = nums[i] + nums[j] + nums[k] - target
                    if abs(diff) < min_diff:
                        min_diff = abs(diff)
                        result = nums[i] + nums[j] + nums[k]
                    if diff < 0:
                        j += 1
                    elif diff > 0:
                        k -= 1
                    else:
                        return target
            i += 1
        return result

# if __name__ == '__main__':
#     result = Solution1().threeSumClosest([-1, 2, 1, -4], 1)
#     print(result)

s = Solution1()
nums = [-1, 2, 1, -4]
target = 1
assert s.threeSumClosest(nums, target) == 2

See also:

https://leetcode.com/problems/3sum-closest/

https://www.lintcode.com/problem/3sum-closest