package two_sum

import (
	"slices"
)

type Index struct {
	Index int
	Value int
}

func ByValue(a, b Index) int {
	return a.Value - b.Value
}

func ToIndices(list []int) []Index {
	result := []Index{}

	for index, value := range list {
		result = append(result, Index{index, value})
	}

	slices.SortFunc(result, ByValue)
	return result
}

// https://leetcode.com/problems/two-sum/description/

func TwoSum(nums []int, target int) []int {
	numbers := ToIndices(nums)
	lower, upper := 0, len(numbers)-1

	for lower < upper {
		current_sum := numbers[lower].Value + numbers[upper].Value

		if current_sum < target {
			lower++
		} else if current_sum > target {
			upper--
		} else {
			return []int{
				numbers[lower].Index,
				numbers[upper].Index,
			}
		}
	}

	return nil
}