it now passes all tests but still too high for prod

2024/12/s2.c

 #include <err.h>
+#include <limits.h>
 #include <stdio.h>
 #include <stdlib.h>
 #include <string.h>
@@ -6,11 +7,15 @@
 #include "inputs.h"
 
 static unsigned char FF[H][W];
+static unsigned char FF2[H][W];
 #define F(y,x) FF[y][x]
+#define F2w(y,x) FF2[y][x]
+#define F2(y,x) (FF2[y][x] & 0x7FU)
 
 static unsigned long long total = 0;
 
 static void getfield(int y, int x);
+static unsigned int getfield2(int y, int x, unsigned char xc2);
 
 int
 main(void)
@@ -60,10 +65,17 @@ recurse(int y, int x)
 static void
 getfield(int y, int x)
 {
-	int y0, x0;
+	int y0, x0, yl, xl;
+	int extent[H][2];
+	unsigned char xc2;
 
+	for (yl = 0; yl < H; ++yl) {
+		extent[yl][0] = INT_MAX;
+		extent[yl][1] = -1;
+	}
 	oc = F(y, x);
 	xc = oc | 0x80U;
+	xc2 = xc & 0x7FU;
 	area = 0;
 	printf("BEGIN '%c' @ (%d, %d)\n", oc, y, x);
 	reclvl = 0;
@@ -88,6 +100,10 @@ getfield(int y, int x)
 	x0 = x;
 	sides = 1;
  walk_north:
+	if (x < extent[y][0])
+		extent[y][0] = x;
+	if (x > extent[y][1])
+		extent[y][1] = x;
 	printf("│↑(%d, %d) ", y, x);
 	if (F(y - 1, x) != xc) {
 		/* west side ended, north side begins */
@@ -117,6 +133,10 @@ getfield(int y, int x)
 	printf("↑\n");
 	goto walk_north;
  walk_east:
+	if (x < extent[y][0])
+		extent[y][0] = x;
+	if (x > extent[y][1])
+		extent[y][1] = x;
 	printf("│→(%d, %d) ", y, x);
 	if (F(y, x + 1) != xc) {
 		/* north side ended, east side begins */
@@ -142,6 +162,10 @@ getfield(int y, int x)
 	printf("→\n");
 	goto walk_east;
  walk_south:
+	if (x < extent[y][0])
+		extent[y][0] = x;
+	if (x > extent[y][1])
+		extent[y][1] = x;
 	printf("│↓(%d, %d) ", y, x);
 	if (F(y + 1, x) != xc) {
 		/* east side ended, south side begins */
@@ -167,6 +191,10 @@ getfield(int y, int x)
 	printf("↓\n");
 	goto walk_south;
  walk_west:
+	if (x < extent[y][0])
+		extent[y][0] = x;
+	if (x > extent[y][1])
+		extent[y][1] = x;
 	printf("│←(%d, %d) ", y, x);
 	if (F(y, x - 1) != xc) {
 		if (y == y0 && x == x0) {
@@ -198,5 +226,193 @@ getfield(int y, int x)
  walk_finished:
 	printf("└─END '%c' @ (%d, %d) → area %llu, sides %llu\n",
 	    oc, y, x, area, sides);
+	memcpy(FF2, FF, sizeof(FF));
+	for (yl = 0; yl < H; ++yl) {
+		if (!(extent[yl][0] < extent[yl][1]))
+			continue;
+		for (xl = extent[yl][0]; xl <= extent[yl][1]; ++xl)
+			if (F2(yl,xl) != xc2 && !(F2(yl,xl) & 0x20U))
+				sides += getfield2(yl, xl, xc2);
+	}
+	printf("→ area %llu, sides %llu\n", area, sides);
 	total += area * sides;
 }
+
+static unsigned long long area2;
+static unsigned long long sides2;
+
+static int
+recurse2(int y, int x, unsigned char xc2)
+{
+	unsigned char c;
+
+	++reclvl;
+	F2w(y, x) |= 0x20U;
+	++area2;
+
+#undef try
+#define try(Y,X,dir) do {					\
+	if ((c = F2(Y, X)) == oc) {				\
+		printf("\t│%*s" dir " recursing @ (%d, %d)\n",	\
+		    reclvl, "", Y, X);				\
+		if (recurse2(Y, X, xc2))			\
+			return (1);				\
+	} else if (c != xc2)					\
+		return (1);					\
+} while (/* CONSTCOND */ 0)
+
+	try(y - 1, x, "up");
+	try(y, x + 1, "right");
+	try(y + 1, x, "down");
+	try(y, x - 1, "left");
+
+	--reclvl;
+	return (0);
+}
+
+static unsigned int
+getfield2(int y, int x, unsigned char xc2)
+{
+	int y0, x0;
+
+	oc = F2(y, x);
+	xc = oc | 0x20U;
+	area2 = 0;
+	printf("\tBEGIN '%c' @ (%d, %d)\n", oc, y, x);
+	reclvl = 0;
+	if (recurse2(y, x, xc2)) {
+		printf("\tNOPE\n");
+		return (0);
+	}
+
+	if (area2 == 1) {
+		/* this uncomplicates the loop below */
+		sides2 = 4;
+		goto walk_finished;
+	}
+ fll:	/* find a lower left corner */
+	if (F2(y + 1, x) == xc) {
+		++y;
+		goto fll;
+	}
+	if (F2(y, x - 1) == xc) {
+		--x;
+		goto fll;
+	}
+	/* now we know a side begins at our left (west) */
+	y0 = y;
+	x0 = x;
+	sides2 = 1;
+ walk_north:
+	printf("\t│↑(%d, %d) ", y, x);
+	if (F2(y - 1, x) != xc) {
+		/* west side ended, north side begins */
+		printf("┌→\n");
+		++sides2;
+		goto walk_east;
+	}
+	--y;
+//	if (y == y0 && x == x0) {
+//		printf("---> (%d, %d) fin\n", y, x);
+//		goto walk_finished;
+//	}
+	if (F2(y, x - 1) == xc) {
+		/* west side ended */
+		/* turn left, go forward (W), south side begins */
+		printf("\033[1m←┐\033[0m\n");
+		--x;
+//		if (y == y0 && x == x0)
+//			goto walk_finished;
+		++sides2;
+		goto walk_west;
+	}
+	if (y == y0 && x == x0) {
+		printf("---> (%d, %d) fin\n", y, x);
+		goto walk_finished;
+	}
+	printf("↑\n");
+	goto walk_north;
+ walk_east:
+	printf("\t│→(%d, %d) ", y, x);
+	if (F2(y, x + 1) != xc) {
+		/* north side ended, east side begins */
+		printf("─┐̬\n");
+		++sides2;
+		goto walk_south;
+	}
+	++x;
+//	if (y == y0 && x == x0) {
+//		printf("---> (%d, %d) fin\n", y, x);
+//		goto walk_finished;
+//	}
+	if (F2(y - 1, x) == xc) {
+		/* north side ended */
+		/* turn left, go forward (N), west side begins */
+		printf("\033[1m─┘̂\033[0m\n");
+		--y;
+		if (y == y0 && x == x0)
+			goto walk_finished;
+		++sides2;
+		goto walk_north;
+	}
+	printf("→\n");
+	goto walk_east;
+ walk_south:
+	printf("\t│↓(%d, %d) ", y, x);
+	if (F2(y + 1, x) != xc) {
+		/* east side ended, south side begins */
+		printf("←┘\n");
+		++sides2;
+		goto walk_west;
+	}
+	++y;
+//	if (y == y0 && x == x0) {
+//		printf("---> (%d, %d) fin\n", y, x);
+//		goto walk_finished;
+//	}
+	if (F2(y, x + 1) == xc) {
+		/* east side ended */
+		/* turn left, go forward (E), north side begins */
+		printf("\033[1m└→\033[0m\n");
+		++x;
+//		if (y == y0 && x == x0)
+//			goto walk_finished;
+		++sides2;
+		goto walk_east;
+	}
+	printf("↓\n");
+	goto walk_south;
+ walk_west:
+	printf("\t│←(%d, %d) ", y, x);
+	if (F2(y, x - 1) != xc) {
+		if (y == y0 && x == x0) {
+			printf("---> (%d, %d) fin\n", y, x);
+			goto walk_finished;
+		}
+		/* south side ended, west side begins */
+		printf("└̂─\n");
+		++sides2;
+		goto walk_north;
+	}
+	--x;
+//	if (y == y0 && x == x0) {
+//		printf("---> (%d, %d) fin\n", y, x);
+//		goto walk_finished;
+//	}
+	if (F2(y + 1, x) == xc) {
+		/* south side ended */
+		/* turn left, go forward (S), east side begins */
+		printf("\033[1m┌̬─\033[0m\n");
+		++y;
+//		if (y == y0 && x == x0)
+//			goto walk_finished;
+		++sides2;
+		goto walk_south;
+	}
+	printf("←\n");
+	goto walk_west;
+ walk_finished:
+	printf("\t└─END '%c' @ (%d, %d) → area %llu, sides %llu\n",
+	    oc, y, x, area2, sides2);
+	return (sides2);
+}