aoc2020/day9/part2/source/app.d

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2020-12-09 14:38:46 +01:00
import std;
import mir.combinatorics;
void main()
{
File("input", "r").byLine.map!(to!long).array.breakXMASEncryption(25).writeln;
}
auto findFirstNumberNotSumOf2PreviousNumbers(long[] numbers, size_t windowSize)
in(numbers.length > windowSize)
{
return numbers.slide(windowSize + 1)
.map!(window => tuple(window[0 .. $ - 1].combinations(2).map!sum, window[windowSize]))
.find!(pair => !pair[0].canFind(pair[1]))
.front[1];
}
unittest
{
long[] input = [
35, 20, 15, 25, 47, 40, 62, 55, 65, 95, 102, 117, 150, 182, 127, 219, 299,
277, 309, 576
];
assert(input.findFirstNumberNotSumOf2PreviousNumbers(5) == 127);
}
auto findContiguousSubrangeWhichSumsTo(long[] input, long number)
{
return iota(2, input.length + 1).map!(i => input.slide(i))
.joiner
.find!(it => it.sum == number)
.front;
}
unittest
{
long[] input = [
35, 20, 15, 25, 47, 40, 62, 55, 65, 95, 102, 117, 150, 182, 127, 219, 299,
277, 309, 576
];
assert(input.findContiguousSubrangeWhichSumsTo(127) == [15, 25, 47, 40]);
}
auto breakXMASEncryption(long[] input, size_t windowSize)
{
auto invalidNumber = input.findFirstNumberNotSumOf2PreviousNumbers(windowSize);
auto contiguousSubrange = input.findContiguousSubrangeWhichSumsTo(invalidNumber);
return contiguousSubrange.minElement + contiguousSubrange.maxElement;
}
unittest
{
long[] input = [
35, 20, 15, 25, 47, 40, 62, 55, 65, 95, 102, 117, 150, 182, 127, 219, 299,
277, 309, 576
];
assert(input.breakXMASEncryption(5) == 62);
}