109 lines
2.2 KiB
Go
109 lines
2.2 KiB
Go
package main
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import (
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"bufio"
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"fmt"
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"os"
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"strconv"
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"time"
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)
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func main() {
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start := time.Now()
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partOne()
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duration := time.Since(start)
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partTwo()
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duration2 := time.Since(start)
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fmt.Printf("p1: %s, p2: %s\n", duration, duration2-duration)
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}
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func makeScanner(test bool) *bufio.Scanner {
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var f *os.File
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if test {
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f, _ = os.Open("inputs/testinput")
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} else {
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f, _ = os.Open("inputs/input")
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}
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reader := bufio.NewReader(f)
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return bufio.NewScanner(reader)
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}
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func partOne() {
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scanner := makeScanner(false)
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r := map[int]int64{} // index => count of 1s
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var lines int64
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for scanner.Scan() {
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line := scanner.Text()
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lines++
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n, _ := strconv.ParseInt(line, 2, 64)
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for i := 0; i < len(line); i++ {
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// check if the number in the i'th column is 1, then bit-shift back to the 1s place to add it if it is
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r[i] += (n & (1 << i)) >> i
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}
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}
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var epsilon, gamma int64
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for i, b := range r {
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// if more than half the bits were ones, gamma gets the 1, otherwise epsilon gets the 1
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// alternatively, this could have been an XOR operation, I suppose, once one or the other had been computed
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if b > lines/2 {
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gamma += 1 << i
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} else {
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epsilon += 1 << i
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}
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}
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fmt.Println(epsilon * gamma)
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}
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func partTwo() {
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scanner := makeScanner(false)
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var lines int
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inputs := map[int]int64{}
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var oxgen, co2scrub int64
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var totalOnes, bitlen int64
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for scanner.Scan() {
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line := scanner.Text()
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n, _ := strconv.ParseInt(line, 2, 64)
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inputs[lines] = n
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bitlen = int64(len(line)) - 1
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totalOnes += n >> (bitlen)
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lines++
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}
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// make initial check
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if totalOnes >= int64(lines)/2 {
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oxgen += (1 << bitlen)
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} else {
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co2scrub += (1 << bitlen)
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}
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for i := bitlen; i > 0; i-- {
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var oxOnes, oxZeroes, coOnes, coZeroes int64
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for _, n := range inputs {
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if oxgen>>i == n>>i {
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if oxgen>>(i-1)^n>>(i-1) == 1 {
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oxOnes++
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} else {
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oxZeroes++
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}
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}
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if co2scrub>>i == n>>i {
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if co2scrub>>(i-1)^n>>(i-1) == 1 {
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coOnes++
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} else {
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coZeroes++
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}
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}
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}
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if oxOnes >= oxZeroes {
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oxgen += (1 << (i - 1))
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}
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if (coZeroes == 0 && coOnes != 0) || (coOnes < coZeroes && coOnes != 0) {
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co2scrub += (1 << (i - 1))
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}
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}
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fmt.Println(oxgen * co2scrub)
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}
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