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@@ -0,0 +1,117 @@
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+package main
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+
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+import (
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+ "bufio"
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+ "errors"
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+ "fmt"
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+ "io"
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+ "log"
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+ "os"
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+ "slices"
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+)
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+
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+func trim(l []byte) []byte {
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+ if len(l) == 0 {
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+ return l
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+ }
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+ if l[len(l)-1] != '\n' {
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+ return l
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+ }
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+ return l[:len(l)-1]
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+}
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+
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+func main() {
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+ width, height := 0, 0
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+ r := bufio.NewReader(os.Stdin)
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+
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+ // Read input
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+ plat := make([]byte, 0, 256)
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+ for {
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+ line, err := r.ReadBytes('\n')
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+ if errors.Is(err, io.EOF) {
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+ break
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+ }
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+ if err != nil {
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+ log.Fatalf("While reading input: %v", err)
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+ }
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+ line = trim(line)
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+ if width == 0 {
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+ width = len(line)
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+ }
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+ if len(line) != width {
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+ log.Fatalf("Expected input line to be of length %d but has length %d", width, len(line))
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+ }
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+ height++
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+ plat = append(plat, line...)
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+ }
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+
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+ // Find regions
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+ regions := make([][]int, 1, 32)
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+ degree := make([]int, len(plat))
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+ incidence := make([]int, len(plat))
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+ for i, plot := range plat {
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+ up, lt, rt, dn := i-width, i-1, i+1, i+width
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+
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+ if dn < len(plat) && plot == plat[dn] {
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+ degree[i]++
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+ }
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+ if i/width == rt/width && plot == plat[rt] {
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+ degree[i]++
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+ }
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+ if 0 <= up && plot == plat[up] {
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+ degree[i]++
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+ regionId := incidence[up]
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+ incidence[i] = regionId
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+ regions[regionId] = append(regions[regionId], i)
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+ }
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+ if 0 <= lt && i/width == lt/width && plot == plat[lt] {
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+ degree[i]++
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+ regionId := incidence[lt]
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+ if incidence[i] == 0 {
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+ incidence[i] = regionId
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+ regions[regionId] = append(regions[regionId], i)
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+ continue
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+ }
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+ if incidence[i] == regionId {
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+ continue
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+ }
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+ // If we made it this far, then incidence[i] was just
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+ // set to incidence[plat[up]]. Therefore, plat[up]
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+ // exists.
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+ // Join subregions with different ids.
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+ var src, tgt int
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+ switch {
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+ case regionId < incidence[i]:
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+ tgt, src = regionId, incidence[i]
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+ case regionId > incidence[i]:
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+ src, tgt = regionId, incidence[i]
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+ }
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+ for _, pid := range regions[src] {
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+ incidence[pid] = tgt
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+ regions[tgt] = append(regions[tgt], pid)
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+ }
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+ regions = slices.Delete(regions, src, src+1)
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+ incidence[i] = tgt
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+ continue
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+ }
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+ if incidence[i] > 0 {
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+ continue
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+ }
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+ region := make([]int, 1, 32)
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+ region[0] = i
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+ regions = append(regions, region)
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+ incidence[i] = len(regions) - 1
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+ }
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+ regions = regions[1:]
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+
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+ // Find prices
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+ total := 0
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+ for _, r := range regions {
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+ perimeter := 0
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+ for _, pid := range r {
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+ perimeter += 4 - degree[pid]
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+ }
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+ total += len(r) * perimeter
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+ }
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+ fmt.Printf("%d\n", total)
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+}
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