From e3fa47e07151345e7cf6d924a309664f0a534619 Mon Sep 17 00:00:00 2001
From: "Alexander \"Arav\" Andreev" <me@arav.su>
Date: Wed, 6 Dec 2023 18:56:28 +0400
Subject: [PATCH] Day 6 part 1 complete.

---
 Makefile     |   4 ++
 day6/in.my   |   2 +
 day6/in.test |   2 +
 day6/p1.c    | 121 +++++++++++++++++++++++++++++++++++++++++++++++++++
 4 files changed, 129 insertions(+)
 create mode 100644 day6/in.my
 create mode 100644 day6/in.test
 create mode 100644 day6/p1.c

diff --git a/Makefile b/Makefile
index 2da10eb..92eedd8 100644
--- a/Makefile
+++ b/Makefile
@@ -29,5 +29,9 @@ day5: day5/p1.c day5/p2.c
 	${CC} ${CFLAGS} $@/p1.c -o bin/$@p1
 	${CC} ${CFLAGS} -fopenmp $@/p2.c -o bin/$@p2
 
+day6: day6/p1.c day6/p2.c
+	${CC} ${CFLAGS} $@/p1.c -o bin/$@p1
+#	${CC} ${CFLAGS} $@/p2.c -o bin/$@p2
+
 clean:
 	rm -f bin/day*p*
\ No newline at end of file
diff --git a/day6/in.my b/day6/in.my
new file mode 100644
index 0000000..2eb8017
--- /dev/null
+++ b/day6/in.my
@@ -0,0 +1,2 @@
+Time:        44     89     96     91
+Distance:   277   1136   1890   1768
diff --git a/day6/in.test b/day6/in.test
new file mode 100644
index 0000000..28f5ae9
--- /dev/null
+++ b/day6/in.test
@@ -0,0 +1,2 @@
+Time:      7  15   30
+Distance:  9  40  200
diff --git a/day6/p1.c b/day6/p1.c
new file mode 100644
index 0000000..9c32545
--- /dev/null
+++ b/day6/p1.c
@@ -0,0 +1,121 @@
+#define  _GNU_SOURCE
+#include <stdio.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdint.h>
+#include <stdbool.h>
+
+
+#define ISDIGIT(c) (c >= 0x30 && c <= 0x39)
+
+int64_t parse_number(char *end);
+
+
+int main(int argc, char **argv) {
+    FILE *input;
+    size_t line_buf_length = 0;
+
+    if (argc == 1 || argv[1][0] == '-')
+		input = stdin;
+	else if ((input = fopen(argv[1], "r")) == NULL) {
+		fprintf(stderr, "Cannot open file %s\n", argv[1]);
+		return -1;
+	}
+
+    char *time_line = NULL, *distance_line = NULL;
+    ssize_t time_line_length = 0, distance_line_length = 0;
+
+    if ((time_line_length = getline(&time_line, &line_buf_length, input)) == -1) {
+        fprintf(stderr, "No time line in a file %s.", argv[1]);
+        return -1;
+    }
+
+    if ((distance_line_length = getline(&distance_line, &line_buf_length, input)) == -1) {
+        fprintf(stderr, "No distance line in a file %s.", argv[1]);
+        return -1;
+    }
+
+    uint64_t *times = (uint64_t *) calloc(2, sizeof(uint64_t));
+    uint64_t *distances = (uint64_t *) calloc(2, sizeof(uint64_t));
+
+    ssize_t times_length = 2, distances_length = 2;
+
+    for (ssize_t i = time_line_length-2, j = 0;;) {
+        while (!ISDIGIT(time_line[i])) {
+            --i;
+            if (time_line[i] == ':')
+                goto tl_end;
+        }
+
+        if (j == times_length)
+            times = (uint64_t *) realloc(times, ++times_length * sizeof(uint64_t));
+
+        times[j++] = parse_number(time_line+i);
+
+        while(ISDIGIT(time_line[i])) --i;
+    }
+    tl_end:
+
+    for (ssize_t i = distance_line_length-2, j = 0;;) {
+        while (!ISDIGIT(distance_line[i])) {
+            --i;
+            if (distance_line[i] == ':')
+                goto dl_end;
+        }
+
+        if (j == distances_length)
+            distances = (uint64_t *) realloc(distances, ++distances_length * sizeof(uint64_t));
+
+        distances[j++] = parse_number(distance_line+i);
+
+        while(ISDIGIT(distance_line[i])) --i;
+    }
+    dl_end:
+
+    uint64_t total_ways = 1;
+
+    for (ssize_t i = 0; i < times_length; ++i) {
+        uint64_t tmid = times[i] / 2;
+        uint64_t ways = 0;
+
+        printf(":: %lu\n", times[i]);
+
+        for (uint64_t ht = tmid; ht <= times[i]; ++ht) {
+            if (ht * (times[i] - ht) > distances[i])
+                ++ways;
+            else
+                break;
+        }
+
+        for (uint64_t ht = tmid-1; ht != 0; --ht) {
+            if (ht * (times[i] - ht) > distances[i])
+                ++ways;
+            else
+                break;
+        }
+
+        printf(":: %lu = %lu\n", times[i], ways);
+
+        total_ways *= ways;
+    }
+
+    free(times);
+    free(distances);
+
+    printf("%lu\n", total_ways);
+
+    return 0;
+}
+
+int64_t parse_number(char *end) {
+    int64_t num = 0;
+
+    for (size_t m = 1;; m *= 10) {
+        if (*end>>4 != 0x3)
+            break;
+        num += (*end&0xf) * m;
+        --end;
+    }
+
+    return num;
+}
\ No newline at end of file