day5, part2

day5/dayFive.go

@@ -5,6 +5,7 @@ import (
 	"log"
 	"math"
 	"os"
+	"sort"
 	"strconv"
 	"strings"
 )
@@ -48,7 +49,7 @@ func applyMap(source int, mapping map[int]int) int {
 }
 
 func (a Almanach)locationForSeed(seed int) int {
-	log.Print("starting calc of location for seed %d", seed)
+	// log.Print("starting calc of location for seed %n", seed)
 	soil := a.SeedToSoil.applyMap(seed)
 	fert := a.SoilToFert.applyMap(soil)
 	water := a.FertToWater.applyMap(fert)
@@ -105,17 +106,53 @@ func Run() int {
 
 	result := math.MaxInt
 	log.Print("before seed range")
-	for _, seed := range seeds {
-		log.Printf("checking for seed %d", seed)
-		location := almanach.locationForSeed(seed)
+	seedRanges := make([][]int, 0)
+	for i := 0; i < len(seeds)-1; i += 2 {
+		start := seeds[i]
+		seedRangeLen := seeds[i+1]
+		seedRanges = append(seedRanges, []int{start, start+seedRangeLen})
+	}
+
+	mergedSeedRanges := merge(seedRanges)
+	for _, seedRange := range mergedSeedRanges {
+		log.Printf("starting new range %+v. current min is %n", seedRange, result)
+		for i := seedRange[0]; i <= seedRange[1]; i++ {
+			location := almanach.locationForSeed(i)
 			if location < result {
 				result = location
 			}
 		}
+	}
 
 	return result
 }
 
+// copy from https://codereview.stackexchange.com/questions/259048/merge-intervalsgolang
+func merge(intervals [][]int) [][]int {
+    const start, end = 0, 1
+
+    var merged [][]int
+
+    if len(intervals) > 1 {
+        sort.Slice(intervals, func(i, j int) bool {
+            return intervals[i][start] < intervals[j][start]
+        })
+    }
+
+    for _, interval := range intervals {
+        last := len(merged) - 1
+        if last < 0 || interval[start] > merged[last][end] {
+            merged = append(merged,
+                []int{start: interval[start], end: interval[end]},
+            )
+        } else if interval[end] > merged[last][end] {
+            merged[last][end] = interval[end]
+        }
+    }
+
+    return merged[:len(merged):len(merged)]
+}
+
 func ReadMap(filename string) EfficientMap {
 	log.Printf("reading in map from %s", filename)
 	result := make([]Triplet, 0)