From ebb6d16853a66713fac9edc654b2534282fc2cec Mon Sep 17 00:00:00 2001
From: Alex Karle <alex@alexkarle.com>
Date: Sun, 5 Dec 2021 11:29:26 -0500
Subject: [PATCH] day5: Add C solution! So fast, so clean :)

It's looking like I'm fine at doing C so long as I don't need any
advanced data structures (mutable lists, hashmaps, etc).

I'd like to go back and brush up on both those when I have time. In the
meanwhile, I'll bask in the joy of a 5/b that's 20x faster than b.py!

    $ time 5/b.py < 5/input
    21305
    0m00.69s real     0m00.66s user     0m00.03s system

    $ time 5/b < 5/input
    21305
    0m00.03s real     0m00.01s user     0m00.01s system

Wild, no? It's almost definitely because we preallocate the 1000x1000
array ahead of time (although, if you see my previous commit, 1000x1000
in python wasn't actually faster than the defaultdict, which is odd...)
---
 5/a.c    | 36 ++++++++++++++++++++++++++++++++++++
 5/b.c    | 36 ++++++++++++++++++++++++++++++++++++
 Makefile |  2 +-
 3 files changed, 73 insertions(+), 1 deletion(-)
 create mode 100644 5/a.c
 create mode 100644 5/b.c

diff --git a/5/a.c b/5/a.c
new file mode 100644
index 0000000..7770b68
--- /dev/null
+++ b/5/a.c
@@ -0,0 +1,36 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int main(void) {
+    int grid[1000][1000] = {0};
+
+    int x1, y1, x2, y2;
+    while (scanf("%d,%d -> %d,%d\n", &x1, &y1, &x2, &y2) != EOF) {
+        /* key: for vert/horiz lines doesn't matter which one you
+         * start at (since you draw the same line either way */
+        if (x1 == x2) {
+            int dist = abs(y1 - y2);
+            int start = y1 < y2 ? y1 : y2;
+            for (int i = start; i <= start + dist; i++) {
+                grid[x1][i]++;
+            }
+        } else if (y1 == y2) {
+            int dist = abs(x1 - x2);
+            int start = x1 < x2 ? x1 : x2;
+            for (int i = start; i <= start + dist; i++) {
+                grid[i][y1]++;
+            }
+        }
+    }
+    
+    int count = 0;
+    for (int r = 0; r < 1000; r++) {
+        for (int c = 0; c < 1000; c++) {
+            if (grid[r][c] > 1) {
+                count++;
+            }
+        }
+    }
+    printf("%d\n", count);
+    return 0;
+}
diff --git a/5/b.c b/5/b.c
new file mode 100644
index 0000000..cb6295e
--- /dev/null
+++ b/5/b.c
@@ -0,0 +1,36 @@
+#include <stdio.h>
+#include <stdlib.h>
+
+int grid[1000][1000] = {0};
+
+void draw(int x1, int y1, int x2, int y2) {
+    int r = x1;
+    int c = y1;
+    int rstep = x1 == x2 ? 0 : (x1 < x2 ? 1 : -1);
+    int cstep = y1 == y2 ? 0 : (y1 < y2 ? 1 : -1);
+    while (r != x2 || c != y2) {
+        grid[r][c]++;
+        r += rstep;
+        c += cstep;
+    }
+    /* loop stops before marking last point! */
+    grid[x2][y2]++;
+}
+
+int main(void) {
+    int x1, y1, x2, y2;
+    while (scanf("%d,%d -> %d,%d\n", &x1, &y1, &x2, &y2) != EOF) {
+        draw(x1, y1, x2, y2);
+    }
+    
+    int count = 0;
+    for (int r = 0; r < 1000; r++) {
+        for (int c = 0; c < 1000; c++) {
+            if (grid[r][c] > 1) {
+                count++;
+            }
+        }
+    }
+    printf("%d\n", count);
+    return 0;
+}
diff --git a/Makefile b/Makefile
index 5fe10ec..dcb3500 100644
--- a/Makefile
+++ b/Makefile
@@ -11,7 +11,7 @@
 CFLAGS = -g -O2 -Wall -Wpedantic -Wextra
 DAY = *
 
-TARGETS = 1/a 1/b 2/a 2/b 3/a
+TARGETS = 1/a 1/b 2/a 2/b 3/a 5/a 5/b
 
 .PHONY: build
 build: $(TARGETS)
--
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