75 lines
1.5 KiB
Go
75 lines
1.5 KiB
Go
package main
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import (
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"fmt"
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"os"
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"regexp"
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"strconv"
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"strings"
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)
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type Range struct {
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From int
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To int
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}
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func main() {
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// iterate over all IDs
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var invalidsum int = 0
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ranges := Decode("input.txt")
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for _, i := range ranges {
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fmt.Printf("\niterating over range: %d to %d\n", i.From, i.To)
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// +1 makes the range inclusive
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for x := range i.To-i.From+1 {
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// to get the "real" number as we took it away initially
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num := x+i.From
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// extract half of the number
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numstring := strconv.Itoa(num)
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mid := len(numstring)/2
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// if both halves are the same, it is an invalid number
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if numstring[:mid] == numstring[mid:] {
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fmt.Printf("found invalid id %d\n", num)
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invalidsum = invalidsum + num
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}
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}
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}
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fmt.Println("sum of invalid ids:", invalidsum)
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}
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func Decode(filename string) []Range {
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f, err := os.ReadFile(filename)
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if err != nil {
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panic(err)
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}
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fstring := string(f)
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fromrangeregex := regexp.MustCompile("^[0-9]*")
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torangeregex := regexp.MustCompile("[0-9]*$")
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var ranges []Range
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for _, i := range strings.Split(fstring, ",") {
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// get range from IDs to iterate over
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fromrangestr := fromrangeregex.FindAllString(i, 1)
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torangestr := torangeregex.FindAllString(i, 1)
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var a Range
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fromrange, _ := strconv.Atoi(fromrangestr[0])
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torange, _ := strconv.Atoi(torangestr[0])
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a.From = fromrange
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a.To = torange
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fmt.Printf("\nextracted ranges to iterate over: %d to %d\n", fromrange, torange)
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ranges = append(ranges, a)
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}
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return ranges
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}
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