package q15

import "slices"

func sortAndDedup3(nums []int) []int {
	slices.Sort(nums)
	head, dup := 0, 0
	for i := 1; i < len(nums); i++ {
		if nums[i] == nums[head] {
			dup++
		} else {
			dup = 0
		}
		if dup < 3 {
			head++
			nums[head] = nums[i]
		}
	}
	return nums[:head+1]
}

func threeSum(nums []int) [][]int {
	nums = sortAndDedup3(nums)
	ret := [][]int{}

	appendResult := func(a, b, c int) {
		triplet := []int{a, b, c}
		if len(ret) > 0 && slices.Equal(triplet, ret[len(ret)-1]) {
			return
		}
		ret = append(ret, triplet)
	}

	for i := 0; i < len(nums)-2; i++ {
		if nums[i] > 0 {
			break
		}
		wants := -nums[i]
		l, r := i+1, len(nums)-1
		for l < r {
			for l < r && nums[l]+nums[r] > wants {
				r--
			}
			if l < r && nums[l]+nums[r] == wants {
				appendResult(nums[i], nums[l], nums[r])
				r--
			}
			for l < r && nums[l]+nums[r] < wants {
				l++
			}
			if l < r && nums[l]+nums[r] == wants {
				appendResult(nums[i], nums[l], nums[r])
				l++
			}
		}

		// skip same numbers
		for ; i < len(nums)-2 && nums[i] == nums[i+1]; i++ {
		}
	}

	return ret
}

var _ = threeSum