From 42c4beb91067ae38951a4ba363e54730d102cbaf Mon Sep 17 00:00:00 2001
From: Marcin Chrzanowski <marcin.j.chrzanowski@gmail.com>
Date: Fri, 25 Dec 2020 15:06:05 +0100
Subject: Add da 2

---
 02/b.c | 120 +++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 120 insertions(+)
 create mode 100644 02/b.c

(limited to '02/b.c')

diff --git a/02/b.c b/02/b.c
new file mode 100644
index 0000000..1e54cbc
--- /dev/null
+++ b/02/b.c
@@ -0,0 +1,120 @@
+#include <fcntl.h>
+#include <stdio.h>
+#include <stdlib.h>
+#include <sys/types.h>
+#include <sys/stat.h>
+#include <unistd.h>
+
+#define BUF_SIZE (32*8192)
+
+enum State {
+    FIRST_NUMBER,
+    DASH,
+    SECOND_NUMBER,
+    SPACE,
+    LETTER,
+    COLON,
+    SPACE2,
+    PASSWORD,
+    EOL,
+    EOI
+};
+
+struct state {
+    enum State s;
+    char letter;
+    char pos1;
+    char pos2;
+    char current_pos;
+    char matches;
+};
+
+char buffer[BUF_SIZE];
+
+void parse_byte(struct state *state, char c) {
+    switch (state->s) {
+    case PASSWORD:
+password:
+        state->current_pos++;
+        if (c == '\n') {
+            state->s = EOL;
+        } else if (state->letter == c && (state->current_pos == state->pos1 || state->current_pos == state->pos2)) {
+            state->matches++;
+        }
+        
+        break;
+    case FIRST_NUMBER:
+        if (c == '-') {
+            state->s = DASH;
+        } else {
+            int digit = c-'0';
+            state->pos1 *= 10;
+            state->pos1 += digit;
+        }
+        break;
+    case DASH:
+        state->s = SECOND_NUMBER;
+    case SECOND_NUMBER:
+        if (c == ' ') {
+            state->s = SPACE;
+        } else {
+            int digit = c-'0';
+            state->pos2 *= 10;
+            state->pos2 += digit;
+        }
+        break;
+    case SPACE:
+        state->letter = c;
+        state->s = LETTER;
+        break;
+    case LETTER:
+        state->s = COLON;
+        break;
+    case COLON:
+        state->s = SPACE2;
+        break;
+    case SPACE2:
+        state->s = PASSWORD;
+        goto password;
+    }
+}
+
+int count_correct() {
+    int fd = open("input.txt", O_RDONLY);
+    struct state state;
+    state.s = FIRST_NUMBER;
+    state.pos1 = 0;
+    state.pos2 = 0;
+    state.letter = '\0';
+    state.current_pos = 0;
+    state.matches = 0;
+    int count = 0;
+
+    while (state.s != EOI) {
+        ssize_t bytes = read(fd, buffer, BUF_SIZE);
+
+        if (bytes == 0) {
+            state.s = EOI;
+        }
+
+        for (int i = 0; i < bytes; i++) {
+            parse_byte(&state, buffer[i]);
+            if (state.s == EOL) {
+                if (state.matches == 1) {
+                    count++;
+                }
+                state.s = FIRST_NUMBER;
+                state.pos1 = 0;
+                state.pos2 = 0;
+                state.letter = '\0';
+                state.current_pos = 0;
+                state.matches = 0;
+            }
+        }
+    }
+    return count;
+}
+
+int main() {
+    printf("%d\n", count_correct());
+}
-- 
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