LeetCode 15 输入无序、有重复，输出排重版 3-Sum

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
	}
}