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127 lines
2.2 KiB
127 lines
2.2 KiB
package adventoc2024
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import (
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"bufio"
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"fmt"
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"io"
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"slices"
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"strings"
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)
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type Day2 struct{}
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func (d Day2) Part1(r io.Reader) string {
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s := bufio.NewScanner(r)
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var sum int
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for s.Scan() {
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sz := strings.Count(s.Text(), " ") + 1
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level := make([]int, sz)
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levelprts := make([]any, sz)
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for i := range levelprts {
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levelprts[i] = &level[i]
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}
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fmt.Sscan(s.Text(), levelprts...)
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if layerOk(level) {
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sum++
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} else {
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slices.Reverse(level)
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if layerOk(level) {
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sum++
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}
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}
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}
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return printi(sum)
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}
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// part 2 does not yet work because this code makes a false assumption.
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// that assumption is that in order to fix a broken level, you can only skip the
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// one that made it broken.
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//
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// this is not true because of the following level
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// 5 6 3 2
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// 5 and 6 would be OK, so the algorithm will blame the 3 and attempt to skip it.
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// the real solution however, is to skip the 6 because it would be fine if all descending
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func (d Day2) Part2(r io.Reader) string {
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s := bufio.NewScanner(r)
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var sum int
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Scan:
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for s.Scan() {
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sz := strings.Count(s.Text(), " ") + 1
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level := make([]int, sz)
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levelprts := make([]any, sz)
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for i := range levelprts {
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levelprts[i] = &level[i]
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}
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fmt.Sscan(s.Text(), levelprts...)
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increasing := level[1]-level[0] > 0
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var dampened bool
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if increasing {
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for i := 0; i < len(level)-1; i++ {
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if diff := level[i+1] - level[i]; !inrange(diff) {
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if dampened {
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continue Scan
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}
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if i+2 > len(level)-1 {
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continue Scan
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}
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d2 := level[i+2] - level[i]
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if !inrange(d2) {
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continue Scan
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}
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dampened = true
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i++
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}
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}
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sum++
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} else {
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for i := 0; i < len(level)-1; i++ {
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if diff := level[i] - level[i+1]; !inrange(diff) {
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if dampened {
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continue Scan
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}
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if i+2 > len(level)-1 {
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continue Scan
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}
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d2 := level[i] - level[i+2]
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if !inrange(d2) {
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continue Scan
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}
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dampened = true
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i++
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}
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}
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sum++
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}
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}
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return printi(sum)
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}
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func inrange(i int) bool {
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return i < 4 && i > 0
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}
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func layerOk(layer []int) bool {
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for i := 0; i < len(layer)-1; i++ {
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if !inrange(layer[i] - layer[i+1]) {
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return false
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}
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}
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return true
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}
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