3Sum Closest

Given an integer array nums of length n and an integer target, find three integers in nums such that the sum is closest to 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: The sum that is closest to the target is 2. (-1 + 2 + 1 = 2).

Example 2:

Input: nums = [0,0,0], target = 1
Output: 0

 

Constraints:

  • 3 <= nums.length <= 1000
  • -1000 <= nums[i] <= 1000
  • -104 <= target <= 104
SOLUTION:
class Solution:
    def threeSumClosest(self, nums: List[int], target: int) -> int:
        n = len(nums)
        if n < 3:
            return []
        nums = [3 * num - target for num in nums]
        nums.sort()
        closest = float('inf')
        for i in range(n - 2):
            a = nums[i]
            start = i + 1
            end = n - 1
            while start < end:
                b = nums[start]
                c = nums[end]
                total = a + b + c
                if abs(total) < abs(closest):
                    closest = total
                if total > 0:
                    end -= 1
                else:
                    start += 1
        return target + closest // 3

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