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day12.go
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day12.go
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// Copyright 2021 Google LLC
//
// Licensed under the Apache License, Version 2.0 (the "License");
// you may not use this file except in compliance with the License.
// You may obtain a copy of the License at
//
// http://www.apache.org/licenses/LICENSE-2.0
//
// Unless required by applicable law or agreed to in writing, software
// distributed under the License is distributed on an "AS IS" BASIS,
// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
// See the License for the specific language governing permissions and
// limitations under the License.
// Package day12 solves AoC 2017 day 12.
package day12
import (
"fmt"
"strings"
"github.com/fis/aoc/glue"
"github.com/fis/aoc/util"
"github.com/fis/aoc/util/graph"
)
func init() {
glue.RegisterSolver(2017, 12, glue.LineSolver(solve))
}
func solve(lines []string) ([]string, error) {
g, err := buildGraph(lines)
if err != nil {
return nil, err
}
vertGroup, groupVerts := partition(g)
zero, ok := g.V("0")
if !ok {
return nil, fmt.Errorf("no vertex 0 in graph")
}
p1 := len(groupVerts[vertGroup[zero]])
p2 := len(groupVerts)
return glue.Ints(p1, p2), nil
}
func partition(g *graph.Sparse) (vertGroup map[int]int, groupVerts map[int][]int) {
vertGroup = make(map[int]int)
groupVerts = make(map[int][]int)
for startV := 0; startV < g.Len(); startV++ {
if _, found := vertGroup[startV]; found {
continue
}
group := len(groupVerts)
edge := []int{startV}
for len(edge) > 0 {
at := edge[len(edge)-1]
edge = edge[:len(edge)-1]
if _, found := vertGroup[at]; found {
continue
}
vertGroup[at] = group
groupVerts[group] = append(groupVerts[group], at)
for it := g.Succ(at); it.Valid(); it = g.Next(it) {
_, toV := it.At()
if _, found := vertGroup[toV]; !found {
edge = append(edge, toV)
}
}
}
}
return vertGroup, groupVerts
}
func buildGraph(lines []string) (*graph.Sparse, error) {
g := graph.NewBuilder()
for _, line := range lines {
from, tos, ok := strings.Cut(line, " <-> ")
if !ok {
return nil, fmt.Errorf("bad line: missing <->: %s", line)
}
u := g.V(from)
for s := util.Splitter(tos); !s.Empty(); {
to := s.Next(", ")
v := g.V(to)
g.AddEdge(u, v)
}
}
return g.SparseDigraph(), nil
}