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48 lines
1.3 KiB
Go
48 lines
1.3 KiB
Go
package main
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const CYCLES = 1000000000
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// cycleOnce transposes and rolls a single image four times (N,W,S,E)
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func cycleOnce(image img) {
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for i := 0; i < 4; i++ {
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for i, line := range image.transposed() {
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image.raw[i] = rollRight(line)
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}
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}
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}
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// cycleMany cycles a single image for a given number of iterations
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// it caches seen images as well as their location in the period
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// finally it copies the cached image with idx matching the interval to image.raw
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func cycleMany(image img, iterations int) {
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cachedIndexes := make(map[string]int)
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cachedImages := make(map[int][]string)
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i, start := 0, 0
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for ; i < iterations; i++ {
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cycleOnce(image)
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if idx, ok := cachedIndexes[image.String()]; ok { // we found first repeated image
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start = idx
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i++
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break
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}
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cachedIndexes[image.String()] = i + 1
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cachedImages[i+1] = make([]string, len(image.raw))
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copy(cachedImages[i+1], image.raw)
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}
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period := i - start // length of a full period
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copy(image.raw, cachedImages[start+((iterations-i-1)%period)+1]) // copy cachedImage into image.raw
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}
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// two returns the load of all boulders after 1000000000 cycles
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func two(lines []string) int {
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image := newImg(len(lines))
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copy(image.raw, lines)
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cycleMany(image, CYCLES)
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return getload(image.transposed())
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}
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