advent-of-code/2023/day05_almanac.go

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package _023
import (
"bufio"
"io"
"slices"
"strings"
)
func Day05Part1(input io.Reader) (int, error) {
scanner := bufio.NewScanner(input)
scanner.Scan()
seeds := lineToInts(strings.TrimPrefix(scanner.Text(), "seeds: "))
scanner.Scan()
inMap := false
var currentMap day05Map
for scanner.Scan() {
line := scanner.Text()
if line == "" {
for i, seed := range seeds {
seeds[i] = currentMap.convert(seed)
}
inMap = false
currentMap = nil
} else if strings.HasSuffix(line, "map:") {
inMap = true
} else if inMap {
currentMap = append(currentMap, newDay05Range(line))
}
}
if inMap {
// Convert one last time if necessary
for i, seed := range seeds {
seeds[i] = currentMap.convert(seed)
}
}
return slices.Min(seeds), nil
}
func Day05Part2(input io.Reader) (int, error) {
scanner := bufio.NewScanner(input)
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scanner.Scan()
seedRanges := parseSeedRanges(lineToInts(strings.TrimPrefix(scanner.Text(), "seeds: ")))
scanner.Scan()
inMap := false
var currentMap day05Map
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for scanner.Scan() {
line := scanner.Text()
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if line == "" {
var newRanges []day05SeedRange
for _, sRange := range seedRanges {
newRanges = append(newRanges, currentMap.convertRange(sRange)...)
}
seedRanges = newRanges
inMap = false
currentMap = nil
} else if strings.HasSuffix(line, "map:") {
inMap = true
} else if inMap {
currentMap = append(currentMap, newDay05Range(line))
}
}
if inMap {
// Convert one last time if necessary
var newRanges []day05SeedRange
for _, sRange := range seedRanges {
newRanges = append(newRanges, currentMap.convertRange(sRange)...)
}
seedRanges = newRanges
inMap = false
currentMap = nil
}
mini := int(^uint(0) >> 1) // highest int
for _, r := range seedRanges {
if r.start < mini {
mini = r.start
}
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}
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return mini, nil
}
func parseSeedRanges(ints []int) []day05SeedRange {
ranges := make([]day05SeedRange, len(ints)/2)
for i := 0; i < len(ints)-1; i += 2 {
ranges[i/2] = day05SeedRange{start: ints[i], end: ints[i] + ints[i+1]}
}
return ranges
}
// range is [start; end)
// start is included, end is not.
type day05SeedRange struct {
start, end int
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}
type day05Range struct {
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destStart, sourceStart, length int
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}
func newDay05Range(line string) day05Range {
ints := lineToInts(line)
return day05Range{
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destStart: ints[0],
sourceStart: ints[1],
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length: ints[2],
}
}
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func (r day05Range) sourceEnd() int {
return r.sourceStart + r.length
}
func (r day05Range) destEnd() int {
return r.destStart + r.length
}
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func (r day05Range) convert(n int) (int, bool) {
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if n >= r.sourceStart && n < r.sourceEnd() {
return r.mustConvert(n), true
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}
return n, false
}
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func (r day05Range) mustConvert(n int) int {
return n - r.sourceStart + r.destStart
}
func (r day05Range) convertRange(s day05SeedRange) (converted []day05SeedRange, notConverted []day05SeedRange) {
if r.sourceStart <= s.start && s.end <= r.sourceEnd() {
// s-----s
// r--------r
return []day05SeedRange{{start: r.mustConvert(s.start), end: r.mustConvert(s.end)}}, nil
} else if s.start < r.sourceStart && r.sourceStart <= s.end && s.end <= r.sourceEnd() {
// s-------s
// r--------r
return []day05SeedRange{{start: r.destStart, end: r.mustConvert(s.end)}}, []day05SeedRange{{start: s.start, end: r.sourceStart}}
} else if r.sourceStart <= s.start && s.start <= r.sourceEnd() && r.sourceEnd() < s.end {
// s-------s
// r--------r
return []day05SeedRange{{start: r.mustConvert(s.start), end: r.destEnd()}}, []day05SeedRange{{start: r.sourceEnd(), end: s.end}}
} else if s.start <= r.sourceStart && r.sourceEnd() < s.end {
// s------------s
// r--------r
return []day05SeedRange{{start: r.destStart, end: r.destEnd()}}, []day05SeedRange{{start: s.start, end: r.sourceStart}, {start: r.sourceEnd(), end: s.end}}
} else {
// s---s
// r-----r
return nil, []day05SeedRange{s}
}
}
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type day05Map []day05Range
func (m day05Map) convert(n int) int {
for _, dRange := range m {
if conv, ok := dRange.convert(n); ok {
return conv
}
}
return n
}
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func (m day05Map) convertRange(s day05SeedRange) []day05SeedRange {
var converted []day05SeedRange
toConvert := []day05SeedRange{s}
for _, dRange := range m {
var toConvertNext []day05SeedRange
for _, c := range toConvert {
var conv []day05SeedRange
conv, toConvertNext = dRange.convertRange(c)
converted = append(converted, conv...)
}
toConvert = toConvertNext
}
converted = append(converted, toConvert...)
return converted
}