/
main.go
59 lines (45 loc) · 849 Bytes
/
main.go
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package main
import (
"bufio"
"fmt"
"io"
"os"
"path"
"strconv"
)
func input() *os.File {
input, err := os.Open(path.Join("2020", "1", "input.txt"))
if err != nil {
panic(err)
}
return input
}
func parse(r io.Reader) map[int]bool {
expenses := make(map[int]bool)
scanner := bufio.NewScanner(r)
for scanner.Scan() {
expense, err := strconv.Atoi(scanner.Text())
if err != nil {
panic(err)
}
expenses[expense] = true
}
if scanner.Err() != nil {
panic(scanner.Err())
}
return expenses
}
func solve(expenses map[int]bool) int {
const target = 2020
for expense := range expenses {
// look for whether the other needed value exists
needed := target - expense
if _, ok := expenses[needed]; ok {
return expense * needed
}
}
panic("no matches")
}
func main() {
fmt.Println(solve(parse(input())))
}