1 files changed, 48 insertions, 0 deletions
diff --git a/aoc/2021/05/part-two.zig b/aoc/2021/05/part-two.zig
new file mode 100644
index 0000000..2c7ed83
--- /dev/null
+++ b/aoc/2021/05/part-two.zig
@@ -0,0 +1,48 @@
+const allocator = std.heap.page_allocator;
+const parseUnsigned = std.fmt.parseUnsigned;
+const print = std.debug.print;
+const set = std.mem.set;
+const swap = std.mem.swap;
+const std = @import("std");
+const tokenize = std.mem.tokenize;
+
+inline fn index(x: usize, y: usize) usize {
+    return x * 1000 + y;
+}
+
+pub fn main() !void {
+    const diagram = try allocator.alloc(u16, 1_000_000);
+    defer allocator.free(diagram);
+    set(u16, diagram, 0);
+
+    var input = tokenize(@embedFile("input"), "\n");
+    while (input.next()) |line| {
+        var segment = tokenize(line, " -> ");
+        var point = tokenize(segment.next().?, ",");
+        var x1 = try parseUnsigned(usize, point.next().?, 10);
+        var y1 = try parseUnsigned(usize, point.next().?, 10);
+        point = tokenize(segment.next().?, ",");
+        var x2 = try parseUnsigned(usize, point.next().?, 10);
+        var y2 = try parseUnsigned(usize, point.next().?, 10);
+
+        if (x1 == x2) {
+            if (y1 > y2) swap(usize, &y1, &y2);
+            while (y1 <= y2) : (y1 += 1)
+                diagram[index(x1, y1)] += 1;
+        } else if (y1 == y2) {
+            if (x1 > x2) swap(usize, &x1, &x2);
+            while (x1 <= x2) : (x1 += 1)
+                diagram[index(x1, y1)] += 1;
+        } else while (true) {
+            diagram[index(x1, y1)] += 1;
+            if (x1 == x2 or y1 == y2) break;
+            if (x1 > x2) x1 -= 1 else x1 += 1;
+            if (y1 > y2) y1 -= 1 else y1 += 1;
+        }
+    }
+
+    var result: usize = 0;
+    for (diagram) |point|
+        result += @boolToInt(point > 1);
+    print("{}\n", .{ result });
+}