48 lines
No EOL
1.1 KiB
Kotlin
48 lines
No EOL
1.1 KiB
Kotlin
fun main() {
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val grid = Grid.read("day4.txt")
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val part1 = grid.all().fold(0) { acc, line ->
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val string = line.joinToString(separator = "")
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acc + string.countSubstring("XMAS") + string.countSubstring("SAMX")
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}
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println("Part 1: $part1")
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var part2 = 0
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for (y in 1..<(grid.height - 1)) {
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val row = grid.rows[y]
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part2 += row.indices.filter { it > 0 && it < grid.width - 1 && row[it] == 'A' }
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.count { grid.xmasAt(it, y) }
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}
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println("Part 2: $part2")
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}
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fun Grid.xmasAt(x: Int, y: Int): Boolean {
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assert(get(x, y) == 'A')
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val tl = get(x - 1, y - 1)
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val tr = get(x + 1, y - 1)
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val bl = get(x - 1, y + 1)
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val br = get(x + 1, y + 1)
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val d1 = (tl == 'M' && br == 'S') || (tl == 'S' && br == 'M')
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val d2 = (bl == 'M' && tr == 'S') || (bl == 'S' && tr == 'M')
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return d1 && d2
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}
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fun String.countSubstring(substring: String): Int {
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var start = 0
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var count = 0
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while (true) {
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val next = indexOf(substring, start)
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if (next == -1) break
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count++
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start = next + substring.length
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}
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return count
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} |