adventofcode/2018/day02-2.go

// This is my second solution, c.f. https://github.com/annabunches/adventofcode/commit/3ca1a1068b749bab4d0626af32549ce2385d57bb
// for the original solution.
//
// This solution is far more elegant; it runs in O(n*m) time, instead of the original implementation's O(n^2 * m) time.
// Thanks to @lizthegrey for (probably unintentionally) prompting me to rewrite this >_>
package main

import (
	"fmt"

	"internal/util"
)

func main() {
	ids := util.ReadInput()
	subIDs := make(map[string]struct{})

	for _, id := range ids {
		// iterate over each letter
		for i := range id {
			// create a subID with just letter id[i] omitted
			subID := id[0:i] + id[i+1:]

			// if it's already in our map, we've found the correct output
			if _, found := subIDs[subID]; found {
				fmt.Println(subID)
				return
			}

			// otherwise, add the substring to our map
			subIDs[subID] = struct{}{}
		}
	}
}