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day05.go
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day05.go
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// Copyright 2020 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 day05 solves AoC 2018 day 5.
package day05
import (
"fmt"
"github.com/fis/aoc/glue"
)
func init() {
glue.RegisterSolver(2018, 5, glue.LineSolver(solve))
}
func solve(lines []string) ([]string, error) {
if len(lines) != 1 {
return nil, fmt.Errorf("expecting only 1 line of input, got %d", len(lines))
}
p1 := reducedLen(lines[0])
p2 := improve(lines[0])
return glue.Ints(p1, p2), nil
}
func reducedLen(polymer string) int {
buf := reduce([]byte(polymer))
return len(buf)
}
func reduce(polymer []byte) []byte {
for {
var i, o int
for i < len(polymer) {
if i+1 < len(polymer) && polymer[i] == unitPairs[polymer[i+1]] {
i += 2
} else {
if o < i {
polymer[o] = polymer[i]
}
i++
o++
}
}
if o < i {
polymer = polymer[:o]
} else {
return polymer
}
}
}
func improve(polymer string) int {
min := len(polymer)
for i := byte(0); i < 26; i++ {
buf := reduce(prune([]byte(polymer), 'a'+i, 'A'+i))
if len(buf) < min {
min = len(buf)
}
}
return min
}
func prune(polymer []byte, u1, u2 byte) []byte {
var i, o int
for i < len(polymer) {
if polymer[i] != u1 && polymer[i] != u2 {
if o < i {
polymer[o] = polymer[i]
}
o++
}
i++
}
return polymer[:o]
}
var unitPairs [256]byte
func init() {
for i := byte(0); i < 26; i++ {
unitPairs['a'+i] = 'A' + i
unitPairs['A'+i] = 'a' + i
}
}