Finish day05, part 2

src/days/day05.zig

@@ -3,20 +3,24 @@ const std = @import("std");
 pub const title = "Day 05: Cafeteria";
 
 pub fn run(allocator: std.mem.Allocator) !void {
-    //const input = @embedFile("./input/day05.txt");
-    const input =
-        \\3-5
-        \\10-14
-        \\16-20
-        \\12-18
-        \\
-        \\1
-        \\5
-        \\8
-        \\11
-        \\17
-        \\32
-        ;
+    const input = @embedFile("./input/day05.txt");
+    //const input =
+    //    \\3-5
+    //    \\10-14
+    //    \\16-20
+    //    \\12-18
+    //    \\
+    //    \\1
+    //    \\5
+    //    \\8
+    //    \\11
+    //    \\17
+    //    \\32
+    //    ;
+    //const input =
+    //    \\383043617664892-389277822354893
+    //    \\387921155483286-389277822354893
+    //    ;
 
     var lines = std.mem.tokenizeScalar(u8, input, '\n');
 
@@ -25,6 +29,7 @@ pub fn run(allocator: std.mem.Allocator) !void {
 
     var accumulator: u64 = 0;
 
+    var i: usize = 0;
     while (lines.next()) |line| {
         var components = std.mem.tokenizeScalar(u8, line, '-');
 
@@ -35,10 +40,13 @@ pub fn run(allocator: std.mem.Allocator) !void {
             .end = try std.fmt.parseUnsigned(u64, end_s, 10),
         };
 
-        const non_overlapping = try processRange(range, ranges.items, &accumulator, allocator);
-        accumulator += (non_overlapping.end + 1) - non_overlapping.start;
+        std.debug.print("==> range {d}\n", .{i});
+
+        processRange(range, ranges.items, &accumulator, 0);
 
         try ranges.append(allocator, range);
+
+        i += 1;
     }
 
     var buffer: [64]u8 = undefined;
@@ -54,52 +62,64 @@ fn processRange(
     range: Range,
     ranges: []Range,
     accumulator: *u64,
-    allocator: std.mem.Allocator,
-) !Range {
+    level: usize,
+) void {
+    for (0..level) |_| std.debug.print("\t", .{});
+    std.debug.print("recursion level = {d}\n", .{level});
+
+    for (0..level) |_| std.debug.print("\t", .{});
     std.debug.print("considering {f}\n", .{range});
 
     var overlapped = false;
     for (ranges) |other| {
-        const overlaps = try range.overlaps(allocator, &other);
-        if (overlaps) |outside| {
-            defer allocator.free(outside);
-
-            std.debug.assert(outside.len <= 2);
-
+        const difference = range.symmetricDifference(other);
+        if (difference.overlapping) {
             overlapped = true;
 
+            if (range.eql(other)) {
+                return;
+            }
+
+            for (0..level) |_| std.debug.print("\t", .{});
             std.debug.print("- overlaps with {f}\n", .{other});
 
-            if (outside.len == 0) {
-                std.debug.print("- overlap is exactly equal\n", .{});
-                return range;
-            }
-
-            var previous_non_overlapping: ?Range = null;
-            for (outside, 0..) |r, i| {
-                std.debug.print("\t+ ({d}) {f} falls outside\n", .{i, r});
-
-                const non_overlapping = try processRange(r, ranges, accumulator, allocator);
-                if ((i + 1) == outside.len) {
-                    return non_overlapping;
+            if (difference.left != null and difference.right != null) {
+                const left = difference.left.?;
+                const right = difference.right.?;
+                for (0..level) |_| std.debug.print("\t", .{});
+                std.debug.print("- left = {f}, right = {f}\n", .{left, right});
+                if (left.eql(right)) {
+                    return;
                 }
-                if (previous_non_overlapping) |p| {
-                    std.debug.print("+ comparing ({f}) to ({f})\n", .{non_overlapping, p});
-                    if (!non_overlapping.eql(&p)) {
-                        return non_overlapping;
-                    }
+
+                if (left.start == range.start) {
+                    processRange(left, ranges, accumulator, level + 1);
+                }
+                if (right.end == range.end) {
+                    processRange(right, ranges, accumulator, level + 1);
+                }
+            } else if (difference.left) |left| {
+                for (0..level) |_| std.debug.print("\t", .{});
+                std.debug.print("- left = {f}\n", .{left});
+                if (left.start == range.start) {
+                    processRange(left, ranges, accumulator, level + 1);
+                }
+            } else if (difference.right) |right| {
+                for (0..level) |_| std.debug.print("\t", .{});
+                std.debug.print("- right = {f}\n", .{right});
+                if (right.end == range.end) {
+                    processRange(right, ranges, accumulator, level + 1);
                 }
-                previous_non_overlapping = non_overlapping;
             }
+            return;
         }
     }
 
     if (!overlapped) {
-        std.debug.print("- no overlap with other range\n", .{});
-        return range;
+        const n = (range.end + 1) - range.start;
+        std.debug.print("- no overlap with other range, adding {d}\n", .{n});
+        accumulator.* += n;
     }
-
-    unreachable;
 }
 
 const Range = struct {
@@ -108,36 +128,55 @@ const Range = struct {
 
     const Self = @This();
 
+    pub const SymmetricDifference = struct {
+        left: ?Self = null,
+        right: ?Self = null,
+        overlapping: bool,
+    };
+
     pub fn format(self: Range, w: *std.io.Writer) std.io.Writer.Error!void {
         try w.print("{d} to {d}", .{self.start, self.end});
     }
 
-    pub fn eql(self: *const Self, other: *const Self) bool {
+    pub fn eql(self: Self, other: Self) bool {
         return self.start == other.start and self.end == other.end;
     }
 
-    pub fn overlaps(self: *const Self, allocator: std.mem.Allocator, other: *const Self) !?[]Self {
-        if (self.start <= other.end and self.end >= other.start) {
-            var l: std.ArrayList(Self) = try .initCapacity(allocator, 2);
-            defer l.deinit(allocator);
-
-            if (self.start < other.start) {
-                try l.append(allocator, Range{ .start = self.start, .end = other.start - 1 });
-            }
-            if (self.end > other.end) {
-                try l.append(allocator, Range{ .start = other.end + 1, .end = self.end });
-            }
-            if (other.start < self.start) {
-                try l.append(allocator, Range{ .start = other.start, .end = self.start - 1 });
-            }
-            if (other.end > self.end) {
-                try l.append(allocator, Range{ .start = self.end + 1, .end = other.end });
-            }
-
-            return try l.toOwnedSlice(allocator);
-        } else {
-            return null;
+    pub fn symmetricDifference(self: Self, other: Self) SymmetricDifference {
+        const overlapping = self.start <= other.end and self.end >= other.start;
+        if (!overlapping) {
+            const left, const right = if (self.end < other.start) .{ self, other } else .{ other, self };
+            return .{
+                .left = left,
+                .right = right,
+                .overlapping = overlapping,
+            };
         }
+
+        var difference: SymmetricDifference = .{ .overlapping = overlapping };
+        if (self.start < other.start) {
+            difference.left = .{
+                .start = self.start,
+                .end = other.start - 1,
+            };
+        } else if (other.start < self.start) {
+            difference.left = .{
+                .start = other.start,
+                .end = self.start - 1,
+            };
+        }
+        if (self.end > other.end) {
+            difference.right = .{
+                .start = other.end + 1,
+                .end = self.end,
+            };
+        } else if (other.end > self.end) {
+            difference.right = .{
+                .start = self.end + 1,
+                .end = other.end,
+            };
+        }
+        return difference;
     }
 };