SHORTEST RANGE IN K SORTED LISTS from https://www.youtube.com/watch?v=zplklOy7ENo, first take (not optimal)

shrange.go

package main

import (
	"fmt"
	"sort"
)

type Slice []int

func (a Slice) Len() int           { return len(a) }
func (a Slice) Swap(i, j int)      { a[i], a[j] = a[j], a[i] }
func (a Slice) Less(i, j int) bool { return a[i] < a[j] }

func validRange(x, y int, k [][]int) (b bool) {
	b = true
	for _, v := range k {
		for _, v := range v {
			if (x <= v) && (v <= y) {
				break
			}
			if v >= y {
				b = false
				break
			}
		}
	}
	return b
}

func joinSlice(k [][]int) []int {
	s := Slice{}
	for _, v := range k {
		s = append(s, v...)
	}
	sort.Sort(s)
	return s
}

func computeRanges(a []int, n int) (k [][]int) {
	for i := 0; i < len(a)-1; i++ {
		for j := i; j < len(a)-1; j++ {
			if j-i <= n {
				k = append(k, []int{a[i], a[j+1]})
			}
		}
	}
	return k
}

func main() {
	k1 := []int{4, 10, 15, 24}
	k2 := []int{0, 9, 19, 20}
	k3 := []int{5, 18, 22, 30}
	k := [][]int{k1, k2, k3}
	// Create a single slice
	singleSlice := joinSlice(k)
	// Compute all the ranges up to len(k) indexes away.
	ranges := computeRanges(singleSlice, len(k))
	// Determine all ranges that cover elements in all slices.
	kf := []int{}
	min := singleSlice[len(singleSlice)-1]
	// Find the min range.
	for _, v := range ranges {
		if validRange(v[0], v[1], k) && (v[1]-v[0] < min) {
			min = v[1] - v[0]
			kf = v
		}
	}
	fmt.Printf("Result: %v\n", kf)
}