solve day 5 part 2

2023/day05_almanac.go

@@ -46,12 +46,63 @@ func Day05Part1(input io.Reader) (int, error) {
 func Day05Part2(input io.Reader) (int, error) {
 	scanner := bufio.NewScanner(input)
 
+	scanner.Scan()
+	seedRanges := parseSeedRanges(lineToInts(strings.TrimPrefix(scanner.Text(), "seeds: ")))
+
+	scanner.Scan()
+
+	inMap := false
+	var currentMap day05Map
 	for scanner.Scan() {
 		line := scanner.Text()
-		_ = line
+		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))
+		}
 	}
 
-	return 0, nil
+	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
+		}
+	}
+
+	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
 }
 
 func lineToInts(line string) []int {
@@ -68,25 +119,61 @@ func lineToInts(line string) []int {
 }
 
 type day05Range struct {
-	destination, source, length int
+	destStart, sourceStart, length int
 }
 
 func newDay05Range(line string) day05Range {
 	ints := lineToInts(line)
 	return day05Range{
-		destination: ints[0],
+		destStart:   ints[0],
-		source:      ints[1],
+		sourceStart: ints[1],
 		length:      ints[2],
 	}
 }
 
+func (r day05Range) sourceEnd() int {
+	return r.sourceStart + r.length
+}
+
+func (r day05Range) destEnd() int {
+	return r.destStart + r.length
+}
+
 func (r day05Range) convert(n int) (int, bool) {
-	if n >= r.source && n < r.source+r.length {
+	if n >= r.sourceStart && n < r.sourceEnd() {
-		return n - r.source + r.destination, true
+		return r.mustConvert(n), true
 	}
 	return n, false
 }
 
+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}
+	}
+}
+
 type day05Map []day05Range
 
 func (m day05Map) convert(n int) int {
@@ -97,3 +184,19 @@ func (m day05Map) convert(n int) int {
 	}
 	return n
 }
+
+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
+}

2023/day05_almanac_test.go

@@ -26,10 +26,38 @@ func TestDay05Part1(t *testing.T) {
 
 func TestDay05Part2(t *testing.T) {
 	tests := []testCase{
-		{"inputs/day05_test2", 0},
+		{"inputs/day05_test2", 46},
-		{"inputs/day05", 0},
+		{"inputs/day05", 78775051},
 	}
 	for _, test := range tests {
 		t.Run(test.filename, check(test, Day05Part2))
 	}
 }
+
+func TestDay05Ranges(t *testing.T) {
+	tests := []struct {
+		name      string
+		dRange    day05Range
+		seedRange day05SeedRange
+		expected  []day05SeedRange
+	}{
+		{
+			"seed included in range",
+			day05Range{0, 5, 5},
+			day05SeedRange{6, 8},
+			[]day05SeedRange{{1, 3}},
+		},
+		{
+			"range included in seed",
+			day05Range{0, 10, 2},
+			day05SeedRange{9, 13},
+			[]day05SeedRange{{0, 2}, {9, 10}, {12, 13}},
+		},
+	}
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			got := day05Map{test.dRange}.convertRange(test.seedRange)
+			assert.Equal(t, test.expected, got)
+		})
+	}
+}

2023/inputs/day05_test2

@@ -0,0 +1,33 @@
+seeds: 79 14 55 13
+
+seed-to-soil map:
+50 98 2
+52 50 48
+
+soil-to-fertilizer map:
+0 15 37
+37 52 2
+39 0 15
+
+fertilizer-to-water map:
+49 53 8
+0 11 42
+42 0 7
+57 7 4
+
+water-to-light map:
+88 18 7
+18 25 70
+
+light-to-temperature map:
+45 77 23
+81 45 19
+68 64 13
+
+temperature-to-humidity map:
+0 69 1
+1 0 69
+
+humidity-to-location map:
+60 56 37
+56 93 4