aoc2024: day 3

1 files changed, 77 insertions, 0 deletions

diff --git a/aoc24/src/day3.zig b/aoc24/src/day3.zig
new file mode 100644
index 0000000..fc1e7a2
--- /dev/null
+++ b/aoc24/src/day3.zig
@@ -0,0 +1,77 @@
+const std = @import("std");
+
+pub fn parse(_: std.mem.Allocator, data: []const u8) ![]const u8 {
+    return data;
+}
+
+pub fn part1(_: std.mem.Allocator, input: []const u8) !u32 {
+    var state: enum { m, u, l, lp, lhs, rhs } = .m;
+    var lhs: u32 = 0;
+    var rhs: u32 = 0;
+    var sum: u32 = 0;
+    for (input) |c| {
+        if (state == .m and c == 'm') {
+            state = .u;
+        } else if (state == .u and c == 'u') {
+            state = .l;
+        } else if (state == .l and c == 'l') {
+            state = .lp;
+        } else if (state == .lp and c == '(') {
+            state = .lhs;
+        } else if (state == .lhs and '0' <= c and c <= '9') {
+            lhs *= 10;
+            lhs += c - '0';
+        } else if (state == .lhs and c == ',') {
+            state = .rhs;
+        } else if (state == .rhs and '0' <= c and c <= '9') {
+            rhs *= 10;
+            rhs += c - '0';
+        } else if (state == .rhs and c == ')') {
+            state = .m;
+            sum += lhs * rhs;
+            lhs = 0;
+            rhs = 0;
+        } else {
+            lhs = 0;
+            rhs = 0;
+            state = .m;
+        }
+    }
+    return sum;
+}
+
+test "part 2" {
+    std.debug.assert(try part2(undefined, "xmul(2,4)&mul[3,7]!^don't()_mul(5,5)+mul(32,64](mul(11,8)undo()?mul(8,5))") == 48);
+}
+
+pub fn part2(_: std.mem.Allocator, input: []const u8) !u32 {
+    var sum: u32 = 0;
+    var i: usize = 0;
+    while (i < input.len) : (i += 1) {
+        const mul = std.mem.indexOfPos(u8, input, i, "mul(") orelse input.len;
+        const dont = std.mem.indexOfPos(u8, input, i, "don't()") orelse input.len;
+        i = @min(mul, dont);
+        if (i == input.len) break;
+        if (i == mul) {
+            i += 4;
+            var lhs: u32 = 0;
+            while ('0' <= input[i] and input[i] <= '9') : (i += 1) {
+                lhs = lhs * 10 + input[i] - '0';
+            }
+            if (input[i] != ',') continue;
+            i += 1;
+            var rhs: u32 = 0;
+            while ('0' <= input[i] and input[i] <= '9') : (i += 1) {
+                rhs = rhs * 10 + input[i] - '0';
+            }
+            if (input[i] != ')') continue;
+            std.debug.print("sum += mul({},{})\n", .{ lhs, rhs });
+            sum += lhs * rhs;
+        } else {
+            std.debug.assert(i == dont);
+            const do = std.mem.indexOfPos(u8, input, i, "do()") orelse break;
+            i = do + 3;
+        }
+    }
+    return sum;
+}