adventofcode2022/day6/marker.c

#include <stdio.h>
#include <stdlib.h>
#include <string.h>

#define max(a,b) (a >= b ? a : b)
#define START_OF_PACKET 4
#define START_OF_MESSAGE 14
#define WINDOW_SIZE max(START_OF_PACKET, START_OF_MESSAGE)

void shift(char*, char);
int unique(char*, int n);

int main() {
    char buf[WINDOW_SIZE], c;
    memset(buf, 0, WINDOW_SIZE);
    int charNum = 1, result = 0, result2= 0;

    while ((c = getchar()) != EOF) {
        shift(buf, c);
        if (charNum > START_OF_PACKET - 1 && !result && unique(buf + (WINDOW_SIZE - START_OF_PACKET), START_OF_PACKET))  {
            result = charNum;
        }
        if (charNum > START_OF_MESSAGE - 1 && !result2 && unique(buf + (WINDOW_SIZE - START_OF_MESSAGE), START_OF_MESSAGE))  {
            result2 = charNum;
        }
        charNum++;
    }

    printf("Packet: %i\n", result);
    printf("Message: %i\n", result2);
}

void shift(char* buf, char c) {
    for (int i = 0; i < WINDOW_SIZE - 1; i++) {
        buf[i] = buf[i+1];
    }
    buf[WINDOW_SIZE - 1] = c;
}

int unique(char* buf, int n) {
    for(int i = 0; i < n; i++) {
        for (int j = i + 1; j < n; j++) {
            if (buf[i] == buf[j]) {
                return 0;
            }
        }
    }

    return 1;
}