From fcabbd7dec64bbbfc997b0a8f46c2194e2d35557 Mon Sep 17 00:00:00 2001
From: "Alexander \"Arav\" Andreev" <me@arav.su>
Date: Mon, 4 Dec 2023 18:21:52 +0400
Subject: [PATCH] Day 4 part 2 complete!

---
 Makefile  |  2 +-
 day4/p2.c | 89 +++++++++++++++++++++++++++++++++++++++++++++++++++++++
 test      |  5 +++-
 3 files changed, 94 insertions(+), 2 deletions(-)
 create mode 100644 day4/p2.c

diff --git a/Makefile b/Makefile
index 8d1c45d..2488024 100644
--- a/Makefile
+++ b/Makefile
@@ -23,7 +23,7 @@ day3: day3/p1.c day3/p2.c
 
 day4: day4/p1.c day4/p2.c
 	${CC} ${CFLAGS} $@/p1.c -o bin/$@p1
-# ${CC} ${CFLAGS} $@/p2.c -o bin/$@p2
+	${CC} ${CFLAGS} $@/p2.c -o bin/$@p2
 
 clean:
 	rm -f bin/day*p*
\ No newline at end of file
diff --git a/day4/p2.c b/day4/p2.c
new file mode 100644
index 0000000..14378a8
--- /dev/null
+++ b/day4/p2.c
@@ -0,0 +1,89 @@
+#define  _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+
+#define STACK_SZ 256
+
+int32_t parse_number(char *end);
+
+
+int main(int argc, char **argv) {
+    FILE *input;
+    char *line = NULL;
+    size_t line_length = 0;
+
+    if (argc == 1 || argv[1][0] == '-')
+		input = stdin;
+	else if ((input = fopen(argv[1], "r")) == NULL) {
+		printf("Cannot open file %s\n", argv[1]);
+		return -1;
+	}
+
+    uint32_t total_copies = 0;
+
+    size_t winning_numbers_len = 0;
+    int8_t *winning_numbers = NULL;
+    char *colon_pos = NULL, *pipe_pos = NULL;
+
+    uint32_t stack[STACK_SZ] = {0};
+    uint8_t stack_pos = 0;
+
+    while (getline(&line, &line_length, input) != -1) {
+        colon_pos = strchr(line, ':');
+        pipe_pos = strchr(line, '|');
+
+        if (winning_numbers == NULL) {
+            winning_numbers_len = (pipe_pos - colon_pos - 2) / 3;
+            winning_numbers = (int8_t *) calloc(winning_numbers_len, sizeof(int8_t));
+        }
+
+        for (size_t i = 0, wl_pos = (size_t)colon_pos+4; i < winning_numbers_len; ++i, wl_pos += 3) {
+            winning_numbers[i] = parse_number((char *)(wl_pos-1));
+        }
+
+        uint32_t card_copies = 1 + stack[stack_pos++];
+
+        total_copies += card_copies;
+
+        size_t old_sp = stack_pos;
+
+        for (char *n_pos = pipe_pos + 4;; n_pos += 3) {
+            int8_t n = parse_number(n_pos-1);
+            for (size_t i = 0; i < winning_numbers_len; ++i) {
+                if (n != winning_numbers[i])
+                    continue;
+                stack[stack_pos++] += card_copies;
+                break;
+            }
+            if (*n_pos == '\n')
+                break;
+        }
+
+        stack_pos = old_sp;
+
+        memset(line, 0, line_length);
+    }
+
+    free(winning_numbers);
+
+    printf("%d\n", total_copies);
+
+    return 0;
+}
+
+int32_t parse_number(char *end) {
+    int32_t num = 0;
+
+    for (size_t n = 1;; n *= 10) {
+        if (*end>>4 != 0x3)
+            break;
+        num += (*end&0xf) * n;
+        --end;
+    }
+
+    return num;
+}
\ No newline at end of file
diff --git a/test b/test
index 0f46b94..2c68456 100755
--- a/test
+++ b/test
@@ -13,4 +13,7 @@ echo "Day 2 with test data part 1 $(test_case 2 1 "test" "8"), and part 2 $(test
 echo "Day 2 with my data part 1 $(test_case 2 1 "my" "2727"), and part 2 $(test_case 2 2 "my" "56580").";
 
 echo "Day 3 with test data part 1 $(test_case 3 1 "test" "4361"), and part 2 $(test_case 3 2 "test" "467835").";
-echo "Day 3 with my data part 1 $(test_case 3 1 "my" "550934"), and part 2 $(test_case 3 2 "my" "81997870").";
\ No newline at end of file
+echo "Day 3 with my data part 1 $(test_case 3 1 "my" "550934"), and part 2 $(test_case 3 2 "my" "81997870").";
+
+echo "Day 4 with test data part 1 $(test_case 4 1 "test" "13"), and part 2 $(test_case 4 2 "test" "30").";
+echo "Day 4 with my data part 1 $(test_case 4 1 "my" "21959"), and part 2 $(test_case 4 2 "my" "5132675").";
\ No newline at end of file