Day 8

AdventOfCode2023/src/day8/day8.zig

@@ -0,0 +1,111 @@
+const std = @import("std");
+const print = std.debug.print;
+
+fn gcd(a: usize, b: usize) usize {
+    if (b == 0) {
+        return a;
+    }
+    return gcd(b, a % b);
+}
+
+fn lcm(a: usize, b: usize) usize {
+    return (a / gcd(a, b)) * b;
+}
+
+const TreeishNode = struct {
+    label: []const u8,
+    left: ?(*TreeishNode),
+    right: ?(*TreeishNode),
+};
+
+pub fn solve(input: [][]const u8) !void {
+    var allocator = std.heap.page_allocator;
+
+    var instructions = input[0];
+
+    var map = input[1..];
+
+    var nodeMap = std.StringHashMap(*TreeishNode).init(allocator);
+    defer nodeMap.deinit();
+
+    for (map) |line| {
+        var label = line[0..3];
+
+        var node = try allocator.create(TreeishNode);
+        node.label = label;
+        node.left = undefined;
+        node.right = undefined;
+        try nodeMap.put(label, node);
+    }
+
+    for (map) |line| {
+        var label = line[0..3];
+        var left = line[7..10];
+        var right = line[12..15];
+
+        var labelNode = nodeMap.get(label).?;
+        var leftNode = nodeMap.get(left).?;
+        var rightNode = nodeMap.get(right).?;
+
+        labelNode.*.left = leftNode;
+        labelNode.*.right = rightNode;
+    }
+
+    // var starting: []const u8 = "AAA";
+    // var part1: usize = 0;
+    //
+    // while (!std.mem.eql(u8, starting, "ZZZ")) {
+    //     for (instructions) |letter| {
+    //         part1 += 1;
+    //         var current = nodeMap.get(starting).?;
+    //         if (letter == 'R') {
+    //             starting = current.*.right.?.label;
+    //         } else {
+    //             starting = current.*.left.?.label;
+    //         }
+    //     }
+    // }
+
+    var startingPaths = std.ArrayList([]const u8).init(allocator);
+    var pathLength = std.ArrayList(usize).init(allocator);
+
+    defer startingPaths.deinit();
+    defer pathLength.deinit();
+
+    var iter = nodeMap.keyIterator();
+    while (iter.next()) |key| {
+        if (key.*[2] == 'A') {
+            try startingPaths.append(key.*);
+        }
+    }
+
+    for (startingPaths.items) |path| {
+        var s: []const u8 = path;
+        var length: usize = 0;
+
+        while (s[2] != 'Z') {
+            for (instructions) |letter| {
+                length += 1;
+                var current = nodeMap.get(s).?;
+                if (letter == 'R') {
+                    s = current.*.right.?.label;
+                } else {
+                    s = current.*.left.?.label;
+                }
+            }
+        }
+
+        try pathLength.append(length);
+    }
+
+    var lengths = try pathLength.toOwnedSlice();
+    print("{any}\n", .{lengths});
+
+    var part2 = lcm(lengths[0], lengths[1]);
+    for (2..lengths.len) |n| {
+        part2 = lcm(part2, lengths[n]);
+    }
+
+    // print("Part 1: {}\n", .{part1});
+    print("Part 2: {}\n", .{part2});
+}

AdventOfCode2023/src/main.zig

@@ -5,13 +5,14 @@ const std = @import("std");
 // const day4 = @import("./day4/day4.zig");
 // const day5 = @import("./day5/day5.zig");
 // const day6 = @import("./day6/day6.zig");
-const day7 = @import("./day7/day7.zig");
+// const day7 = @import("./day7/day7.zig");
+const day8 = @import("./day8/day8.zig");
 const utils = @import("utils.zig");
 
 pub fn main() !void {
     const allocator = std.heap.page_allocator;
-    var input = try utils.getInput("./src/day7/input.txt", allocator);
+    var input = try utils.getInput("./src/day8/input.txt", allocator);
     defer allocator.free(input);
 
-    try day7.solve(input);
+    try day8.solve(input);
 }