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day06.go
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day06.go
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// Copyright 2022 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 day06 solves AoC 2022 day 6.
package day06
import (
"fmt"
"math/bits"
"github.com/fis/aoc/glue"
)
func init() {
glue.RegisterSolver(2022, 6, glue.LineSolver(solve))
}
func solve(lines []string) ([]string, error) {
if n := len(lines); n != 1 {
return nil, fmt.Errorf("expected 1 line, got %d", n)
}
sig := lines[0]
packet := findMarkerWindowed(sig, 4)
msg := packet - 4 + findMarkerWindowed(sig[packet-4:], 14)
return glue.Ints(packet, msg), nil
}
func findMarkerBitset(sig string, size int) int {
for i := size; i <= len(sig); i++ {
var b uint64
for j := i - size; j < i; j++ {
b |= 1 << (sig[j] & 0x3f)
}
if bits.OnesCount64(b) == size {
return i
}
}
return -1
}
func findMarkerWindowed(sig string, size int) int {
var (
counts [64]int
unique int
)
for i := 0; i < size; i++ {
b := sig[i] & 0x3f
if counts[b] == 0 {
unique++
}
counts[b]++
}
for i := size; i < len(sig); i++ {
if unique == size {
return i
}
out, in := sig[i-size]&0x3f, sig[i]&0x3f
counts[out]--
if counts[out] == 0 {
unique--
}
if counts[in] == 0 {
unique++
}
counts[in]++
}
if unique == size {
return len(sig)
}
return -1
}