79 lines
1.3 KiB
Go
79 lines
1.3 KiB
Go
package year25
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import (
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"fmt"
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"io"
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"git.bizdoc.ro/private/devkit.git/collections/geometry/v2"
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)
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const Day4PaperRoll = '@'
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func Day4Part1(r io.Reader, l Logger) (any, error) {
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// 4 rolls in 8 adjacent positions
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var accessibleRolls int
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g, err := geometry.ReaderToByteGrid(r)
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if err != nil {
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return nil, fmt.Errorf("day4: failed to read grid: %w", err)
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}
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for c := range g.Points() {
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if g.At(c) != Day4PaperRoll {
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continue
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}
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var count int
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for p := range g.SubgridPointsIter(c.MoveUpLeft(), c.MoveDownRight()) {
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if g.At(p) == Day4PaperRoll {
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count += 1
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}
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}
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if count <= 4 {
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accessibleRolls += 1
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}
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}
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return accessibleRolls, nil
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}
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func Day4Part2(r io.Reader, l Logger) (any, error) {
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// 4 rolls in 8 adjacent positions
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var totalRemovedRolls int
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g, err := geometry.ReaderToByteGrid(r)
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if err != nil {
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return nil, fmt.Errorf("day4: failed to read grid: %w", err)
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}
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for {
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removedRolls := 0
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for c := range g.Points() {
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if g.At(c) != Day4PaperRoll {
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continue
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}
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var count int
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for p := range g.SubgridPointsIter(c.MoveUpLeft(), c.MoveDownRight()) {
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if g.At(p) == Day4PaperRoll {
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count += 1
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}
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}
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if count <= 4 {
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removedRolls += 1
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g.Set(c, '.') // remove grid
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}
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}
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if removedRolls == 0 {
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break
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}
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totalRemovedRolls += removedRolls
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}
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return totalRemovedRolls, nil
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}
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