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day09 part2
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xeals 2023-12-09 20:45:13 +11:00
parent 9035d0a8d4
commit 9b8ae4f350
Signed by: xeals
SSH Key Fingerprint: SHA256:53xHRPqZPQewIgPNiVQ96gm8O4xBVzaxNj1LCSJpTf4
1 changed files with 19 additions and 8 deletions
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27
src/day09.zig
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@ -31,7 +31,9 @@ fn zeroed(seq: []const isize) bool {
fn solve(alloc: mem.Allocator, input: []const u8) !Solution { fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
var it = util.splitLines(input); var it = util.splitLines(input);
var sum: isize = 0; var prev_sum: isize = 0;
var next_sum: isize = 0;
while (it.next()) |line| { while (it.next()) |line| {
if (line.len == 0) continue; if (line.len == 0) continue;
var seqs = std.ArrayList([]const isize).init(alloc); var seqs = std.ArrayList([]const isize).init(alloc);
@ -41,17 +43,24 @@ fn solve(alloc: mem.Allocator, input: []const u8) !Solution {
while (!zeroed(seqs.items[seqs.items.len - 1])) { while (!zeroed(seqs.items[seqs.items.len - 1])) {
try seqs.append(try drv(alloc, seqs.items[seqs.items.len - 1])); try seqs.append(try drv(alloc, seqs.items[seqs.items.len - 1]));
} }
// Solve next sequence // Extrapolate
var predicted: isize = 0; var next: isize = 0;
var prev: isize = 0;
for (seqs.items) |seq| {
next += seq[seq.len - 1];
}
for (0..seqs.items.len) |i| {
prev = seqs.items[seqs.items.len - i - 1][0] - prev;
}
for (seqs.items) |seq| { for (seqs.items) |seq| {
predicted += seq[seq.len - 1];
// Clean up // Clean up
alloc.free(seq); alloc.free(seq);
} }
sum += predicted; prev_sum += prev;
next_sum += next;
} }
return .{ .a = sum, .b = 0 }; return .{ .a = next_sum, .b = prev_sum };
} }
test "silver" { test "silver" {
@ -66,8 +75,10 @@ test "silver" {
test "gold" { test "gold" {
const input = const input =
\\ \\0 3 6 9 12 15
\\1 3 6 10 15 21
\\10 13 16 21 30 45
; ;
const sln = try solve(std.testing.allocator, input); const sln = try solve(std.testing.allocator, input);
try std.testing.expectEqual(@as(isize, 0), sln.b); try std.testing.expectEqual(@as(isize, 2), sln.b);
} }