62 lines
1.8 KiB
Zig
62 lines
1.8 KiB
Zig
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const std = @import("std");
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pub fn main() void {
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const input = @embedFile("input.asc");
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var iter = std.mem.split(u8, input, "\n");
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var totalPoints: usize = 0;
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while (iter.next()) |round| {
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// Not a valid round. Not necessary, but just in case
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if (round.len < 3) continue;
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if (round[0] < 'A' or round[0] > 'C') continue;
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if (round[2] < 'X' or round[2] > 'Z') continue;
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// Convert letters to numbers
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const them = round[0] - 'A';
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const me = round[2] - 'X';
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// Points per shape chosen is easy.
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// {0,1,2} + 1 == {1,2,3}
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// which is what we want.
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const shapePoints = me+1;
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// Now this is a bit more complex.
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// We notice that 'them - me' gives:
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//
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// tie = 0;
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// die = both -2 or 1;
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// win = both -1 or 2;
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//
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// If we wrap the results (adding 3 before because
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// we can't have negatives) 'result = (result+3)%3'
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// we get
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//
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// tie = 0; -> 3 points
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// die = 1; -> 0 points
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// win = 2; -> 6 points
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//
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// Ideally we would want {0,1,2} to be {0,3,6}, not
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// {3,0,6}. If we adjust it to '(result+4)%3' we get:
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//
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// win = 0; -> 6 points
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// tie = 1; -> 3 points
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// die = 2; -> 0 points
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//
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// That's closer but not ideal. If we invert the
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// numbers then we do get there '2-(result+4)%3':
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//
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// die = 0; -> 0 points
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// tie = 1; -> 3 points
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// win = 2; -> 6 points
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//
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// Now we multiply by three so '(2-(result+4)%3)*3'
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// and boom, points per result per match.
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const resultPoints = (2-((4 + them) - me)%3)*3;
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totalPoints += resultPoints + shapePoints;
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}
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std.debug.print("{}\n", .{totalPoints});
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}
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