// Given a list of integers xs and an integer k, how many (not
// necessarily adjacent) pairs of integers that sum to k can be
// removed from xs?

// An exercise from Leetcode.

// Related to the “two sum” problem, which just asks if any such pairs
// exist: <https://nullprogram.com/blog/2023/06/26/>

// I did this in Golang because Python is IRC-unfriendly, but
// surprisingly it came out to be shorter in Golang than in Python,
// due to Golang being more loosey-goosey about initialization.
package main

func removals(xs []int, k int) (n int) {
	seen := map[int]int{}
	for _, x := range xs {
		if seen[k - x] != 0 {
			seen[k - x]--
			n++
		} else {
			seen[x]++
		}
	}
	return
}

// seen := map[int]int{}; n := 0; for _, x := range xs {y := k - x; if seen[y] != 0 {seen[y]--; n++} else {seen[x]++}}

func main() {
	xs := []int{3, 1, 3, 5, 3}
	println(removals(xs, 6))
}