93 lines
1.5 KiB
Go
93 lines
1.5 KiB
Go
package main
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import (
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"fmt"
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"strconv"
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"github.com/jdkaplan/advent-of-code/aoc"
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)
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const bits = 12
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func part1(lines []string) uint {
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var count [bits]int
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for _, line := range lines {
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for i, char := range line {
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// Fix the index to be from the right
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i := bits - i - 1
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switch char {
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case '0':
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count[i]--
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case '1':
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count[i]++
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default:
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panic(char)
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}
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}
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}
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var gamma uint
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var epsilon uint
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for i, c := range count {
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mask := uint(1 << i)
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if c > 0 {
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gamma |= mask
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epsilon &= ^mask
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} else {
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gamma &= ^mask
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epsilon |= mask
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}
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}
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return gamma * epsilon
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}
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func partition(lines []string, idx int) (zeros []string, ones []string) {
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for _, line := range lines {
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char := line[idx]
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switch char {
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case '0':
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zeros = append(zeros, line)
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case '1':
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ones = append(ones, line)
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default:
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panic(char)
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}
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}
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return
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}
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func mustBin(s string) uint {
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u, err := strconv.ParseUint(s, 2, 0)
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if err != nil {
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panic(err)
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}
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return uint(u)
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}
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func part2(lines []string) int {
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oxy, co2 := lines, lines
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for i := 0; i < bits && len(oxy) > 1; i++ {
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zeros, ones := partition(oxy, i)
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if len(ones) >= len(zeros) {
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oxy = ones
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} else {
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oxy = zeros
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}
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}
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for i := 0; i < bits && len(co2) > 1; i++ {
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zeros, ones := partition(co2, i)
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if len(ones) >= len(zeros) {
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co2 = zeros
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} else {
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co2 = ones
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}
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}
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return int(mustBin(oxy[0]) * mustBin(co2[0]))
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}
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func main() {
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lines := aoc.ReadLines("./input/day3.txt")
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fmt.Println(part1(lines))
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fmt.Println(part2(lines))
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}
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