Given a list of integers nums with at least three elements and an integer target, choose three distinct indices whose values sum as close as possible to target, and return that sum. If two different sums are equally close, return the smaller one.
Examples
Input: nums = [-1, 2, 1, -4], target = 1
Output: 2
Explanation: -1 + 2 + 1 = 2 is one away from 1.
Input: nums = [1, 1, 1, 0], target = 100
Output: 3
Constraints
3 <= len(nums) <= 3000,-10**4 <= nums[i] <= 10**4- Target: O(n^2) time after sorting, O(1) extra space.
Goals
- Fix one element and run a converging two-pointer scan on the rest
- Track the closest sum with a deterministic tie-break