V1 粗暴的遍历，时间复杂度O(N³)

func threeSumClosest(nums []int, target int) int {

	min := 0

	result := 0

	for i := 0; i < len(nums); i++ {

		for j := i + 1; j < len(nums); j++ {

			for k := j + 1; k < len(nums); k++ {

				current := abs(nums[i] + nums[j] + nums[k] - target)

				if k == 2 {

					min = current

					result = nums[i] + nums[j] + nums[k]

				} else if current < min {

					min = current

					result = nums[i] + nums[j] + nums[k]

				}

			}

		}

	}

	return result

}

func abs(x int) int {

	if x < 0 {

		return 0 - x;

	} else {

		return x

	}

}

V2 优化到O(N²)

func threeSumClosest(nums []int, target int) int {

	sort.Ints(nums)

	result := nums[0] + nums[1] + nums[len(nums)-1]

	n := len(nums)

	for i := 0; i < n-2; i++ {

		start := i + 1

		end := n - 1

		for start < end {

			current := nums[i] + nums[start] + nums[end]

			x := current - target

			if abs(x) < abs(result - target) {

				result = current

			}

			if x > 0 {

				end--

			} else if x < 0 {

				start++

			} else {

				break

			}

		}

	}

	return result

}

func abs(x int) int {

	if x < 0 {

		return 0 - x;

	} else {

		return x

	}

}