day 5, part 2 (based on solution for part 1)

day05-hard/build.zig

@@ -0,0 +1,70 @@
+const std = @import("std");
+
+// Although this function looks imperative, note that its job is to
+// declaratively construct a build graph that will be executed by an external
+// runner.
+pub fn build(b: *std.Build) void {
+    // Standard target options allows the person running `zig build` to choose
+    // what target to build for. Here we do not override the defaults, which
+    // means any target is allowed, and the default is native. Other options
+    // for restricting supported target set are available.
+    const target = b.standardTargetOptions(.{});
+
+    // Standard optimization options allow the person running `zig build` to select
+    // between Debug, ReleaseSafe, ReleaseFast, and ReleaseSmall. Here we do not
+    // set a preferred release mode, allowing the user to decide how to optimize.
+    const optimize = b.standardOptimizeOption(.{});
+
+    const exe = b.addExecutable(.{
+        .name = "day05-hard",
+        // In this case the main source file is merely a path, however, in more
+        // complicated build scripts, this could be a generated file.
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    // This declares intent for the executable to be installed into the
+    // standard location when the user invokes the "install" step (the default
+    // step when running `zig build`).
+    b.installArtifact(exe);
+
+    // This *creates* a Run step in the build graph, to be executed when another
+    // step is evaluated that depends on it. The next line below will establish
+    // such a dependency.
+    const run_cmd = b.addRunArtifact(exe);
+
+    // By making the run step depend on the install step, it will be run from the
+    // installation directory rather than directly from within the cache directory.
+    // This is not necessary, however, if the application depends on other installed
+    // files, this ensures they will be present and in the expected location.
+    run_cmd.step.dependOn(b.getInstallStep());
+
+    // This allows the user to pass arguments to the application in the build
+    // command itself, like this: `zig build run -- arg1 arg2 etc`
+    if (b.args) |args| {
+        run_cmd.addArgs(args);
+    }
+
+    // This creates a build step. It will be visible in the `zig build --help` menu,
+    // and can be selected like this: `zig build run`
+    // This will evaluate the `run` step rather than the default, which is "install".
+    const run_step = b.step("run", "Run the app");
+    run_step.dependOn(&run_cmd.step);
+
+    // Creates a step for unit testing. This only builds the test executable
+    // but does not run it.
+    const unit_tests = b.addTest(.{
+        .root_source_file = .{ .path = "src/main.zig" },
+        .target = target,
+        .optimize = optimize,
+    });
+
+    const run_unit_tests = b.addRunArtifact(unit_tests);
+
+    // Similar to creating the run step earlier, this exposes a `test` step to
+    // the `zig build --help` menu, providing a way for the user to request
+    // running the unit tests.
+    const test_step = b.step("test", "Run unit tests");
+    test_step.dependOn(&run_unit_tests.step);
+}

day05-hard/sample.in

@@ -0,0 +1,33 @@
+seeds: 79 14 55 13
+
+seed-to-soil map:
+50 98 2
+52 50 48
+
+soil-to-fertilizer map:
+0 15 37
+37 52 2
+39 0 15
+
+fertilizer-to-water map:
+49 53 8
+0 11 42
+42 0 7
+57 7 4
+
+water-to-light map:
+88 18 7
+18 25 70
+
+light-to-temperature map:
+45 77 23
+81 45 19
+68 64 13
+
+temperature-to-humidity map:
+0 69 1
+1 0 69
+
+humidity-to-location map:
+60 56 37
+56 93 4

day05-hard/src/main.zig

@@ -0,0 +1,234 @@
+const std = @import("std");
+
+fn StackList(comptime T: type, comptime capacity_type: type, comptime capacity: capacity_type) type {
+    return struct {
+        const Self = @This();
+        mem: [capacity]T,
+        length: capacity_type,
+
+        fn add(self: *Self, value: T) void {
+            self.mem[self.length] = value;
+            self.length += 1;
+        }
+
+        fn has(self: *const Self, needle: T) bool {
+            for (0..self.length) |i| {
+                if (self.mem[i] == needle) {
+                    return true;
+                }
+            }
+
+            return false;
+        }
+
+        fn getSlice(self: *Self) []T {
+            //var mem_full_slice = &self.mem;
+            //var mem_slice: []T = mem_full_slice[0..self.length];
+            //return mem_slice;
+            return (&self.mem)[0..self.length];
+        }
+
+        fn reset(self: *Self) void {
+            self.length = 0;
+        }
+
+        fn init() Self {
+            return Self{
+                .mem = undefined,
+                .length = 0,
+            };
+        }
+    };
+}
+
+const Range = struct {
+    start: u64,
+    end: u64,
+
+    fn clear(self: *Range) void {
+        self.start = std.math.maxInt(u64);
+        self.end = std.math.maxInt(u64);
+    }
+};
+
+const StateStorage = StackList(Range, u32, 10_000);
+
+const State = struct {
+    a: StateStorage = StateStorage.init(),
+    b: StateStorage = StateStorage.init(),
+    is_a_current: bool = true,
+
+    fn getCurrent(self: *State) *StateStorage {
+        return switch (self.is_a_current) {
+            true => &self.a,
+            false => &self.b,
+        };
+    }
+
+    fn getPrevious(self: *State) *StateStorage {
+        return switch (self.is_a_current) {
+            true => &self.b,
+            false => &self.a,
+        };
+    }
+
+    fn add(self: *State, value: Range) void {
+        self.getCurrent().*.add(value);
+    }
+
+    fn addMapping(self: *State, destination_start: u64, source_start: u64, range_length: u64) void {
+        const source_end = source_start + range_length;
+        //std.debug.print("processing mapping from {d}-{d} (length {d}) to {d}\n", .{ source_start, source_end, range_length, destination_start });
+        for (self.getPrevious().*.getSlice()) |*range_ptr| {
+            const range = range_ptr.*;
+            //std.debug.print("processing range {d}-{d}\n", .{ range.start, range.end });
+            if (source_start <= range.start) {
+                if (source_end <= range.start) {
+                    // no intersection
+                } else if (source_end < range.end) {
+                    self.add(Range{
+                        .start = destination_start + (range.start - source_start),
+                        .end = destination_start + (source_end - source_start),
+                    });
+                    range_ptr.*.start = source_end;
+                } else {
+                    self.add(Range{
+                        .start = destination_start + (range.start - source_start),
+                        .end = destination_start + (range.end - source_start),
+                    });
+                    range_ptr.*.clear();
+                }
+            } else if (source_start < range.end) {
+                if (source_end < range.end) {
+                    self.add(Range{
+                        .start = destination_start,
+                        .end = destination_start + (source_end - source_start),
+                    });
+
+                    range_ptr.*.end = source_start;
+                    self.getPrevious().*.add(Range{
+                        .start = source_end,
+                        .end = range.end,
+                    });
+                } else {
+                    self.add(Range{
+                        .start = destination_start,
+                        .end = destination_start + (range.end - source_start),
+                    });
+
+                    range_ptr.*.end = source_start;
+                }
+            }
+        }
+    }
+
+    fn finishMappings(self: *State) void {
+        //std.debug.print("previous values: {any}\n", .{self.getPrevious().*.getSlice()});
+        for (self.getPrevious().*.getSlice()) |range| {
+            if (range.start < range.end) {
+                self.add(range);
+            }
+        }
+
+        self.is_a_current = !self.is_a_current;
+        self.getCurrent().*.reset();
+    }
+
+    fn getMinPreviousValue(self: *State) u64 {
+        var previous = self.getPrevious().*;
+        var result: u32 = std.math.maxInt(u32);
+        for (previous.getSlice()) |range| {
+            result = @min(result, range.start);
+        }
+
+        return result;
+    }
+
+    fn debug(self: *State) void {
+        _ = self;
+        //std.debug.print("Current state: {any}, previous state: {any}\n", .{ self.getCurrent().*.getSlice(), self.getPrevious().*.getSlice() });
+    }
+};
+
+fn addDigit(result: anytype, digit: u8) void {
+    result.* = (result.* * 10) + (digit - '0');
+}
+
+fn parseFirstLine(line: []const u8) State {
+    var result = State{};
+
+    var index: usize = 7;
+    while (index < line.len) {
+        var range_start: u64 = 0;
+        var range_length: u64 = 0;
+        while (line[index] != ' ') : (index += 1) {
+            addDigit(&range_start, line[index]);
+        }
+
+        index += 1;
+        while (index < line.len and line[index] != ' ') : (index += 1) {
+            addDigit(&range_length, line[index]);
+        }
+
+        result.add(Range{
+            .start = range_start,
+            .end = range_start + range_length,
+        });
+        index += 1;
+    }
+
+    return result;
+}
+
+fn parseMappingLine(line: []const u8, state: *State) void {
+    var destination_start: u64 = 0;
+    var source_start: u64 = 0;
+    var range_length: u64 = 0;
+
+    var index: usize = 0;
+    while (line[index] != ' ') : (index += 1) {
+        addDigit(&destination_start, line[index]);
+    }
+
+    index += 1;
+    while (line[index] != ' ') : (index += 1) {
+        addDigit(&source_start, line[index]);
+    }
+
+    index += 1;
+    while (index < line.len) : (index += 1) {
+        addDigit(&range_length, line[index]);
+    }
+
+    state.addMapping(destination_start, source_start, range_length);
+}
+
+pub fn main() !void {
+    const stdout = std.io.getStdOut().writer();
+
+    const raw_in = std.io.getStdIn();
+    var buffered_reader = std.io.bufferedReader(raw_in.reader());
+    var reader = buffered_reader.reader();
+
+    var line_buffer: [1000]u8 = undefined;
+    const first_line = (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')).?;
+    var state = parseFirstLine(first_line);
+    state.debug();
+    _ = try reader.readUntilDelimiterOrEof(&line_buffer, '\n');
+    _ = try reader.readUntilDelimiterOrEof(&line_buffer, '\n');
+    state.finishMappings();
+    state.debug();
+    while (try reader.readUntilDelimiterOrEof(&line_buffer, '\n')) |line| {
+        if (line.len != 0) {
+            parseMappingLine(line, &state);
+        } else {
+            _ = try reader.readUntilDelimiterOrEof(&line_buffer, '\n');
+            state.finishMappings();
+            state.debug();
+        }
+    }
+
+    state.finishMappings();
+    state.debug();
+    try stdout.print("{d}\n", .{state.getMinPreviousValue()});
+}