57 lines
1.2 KiB
Go
57 lines
1.2 KiB
Go
package day19
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import (
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"math"
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"tools"
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)
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func getNextIndex(m map[int]int, start, max int) int {
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index := start
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for {
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index++
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if index > max {
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index = 0
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}
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if _, ok := m[index]; ok {
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return index
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}
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}
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}
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func Part1(puzzle tools.AoCPuzzle) interface{} {
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elfCount := puzzle.GetInputInt()
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elfs := make(map[int]int)
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for i := 0; i < elfCount; i++ {
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elfs[i] = 1
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}
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index := 0
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for len(elfs) > 1 {
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nextIndex := getNextIndex(elfs, index, elfCount)
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delete(elfs, nextIndex)
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index = getNextIndex(elfs, nextIndex, elfCount)
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}
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return index + 1
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}
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func Part2(puzzle tools.AoCPuzzle) interface{} {
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elfCount := puzzle.GetInputInt()
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var elfs []int
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for i := 0; i < elfCount; i++ {
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elfs = append(elfs, i+1)
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}
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// Does one half not always eliminate the other half +/- 1? Not Quite!!!
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// Does it eliminate half of the "upper" half? As in "every second one"? Also not Quite!
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// 0..4; 0 eliminates 2 (index + floor(half), 1 eliminates 4 (1 + half(len)), 3 eliminates 1 (index + floor(half))
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// (1:?)2:1:2:1:...until len(2) (start with 1 for equal lens and 2 for unequal lens)
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for len(elfs) > 1 {
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half := int(math.Floor(float64(len(elfs) / 2)))
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elfs = append(elfs, elfs[0])
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elfs = append(elfs[1:half], elfs[half+1:]...)
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}
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return elfs[0]
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}
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