Advent-of-Code/2021/day3/solution-part1.c

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


int main( int argc, char *argv[] ){
	if( argc == 2 ) {

		unsigned int gamma = 0;
		unsigned int epsilon = 0;
		unsigned int lineLength = 0;
		unsigned int noOfLines = 0;

		// Read the values into an array
		FILE *fp=fopen(argv[1], "r");
		char ch = fgetc(fp);
		while ( ch != '\n' ){
			lineLength++;
			ch = fgetc(fp);
		}

		rewind(fp);

		unsigned int digitCount[lineLength];
		memset( &digitCount, 0, lineLength*sizeof(unsigned int) );
		

		for ( int i = 0; !feof(fp); i++){
			ch=fgetc(fp);
			switch (ch) {
				case '\n':
					// I will be incremented at the end of the iteration
					i=-1;
					noOfLines++;
					break;
				case '1':
					digitCount[i]++;
					break;
			}
		}

		for (unsigned int i=0; i < lineLength; i++ ){
			if ( digitCount[i] > ( (double)noOfLines ) / 2 ){
				gamma = gamma | 1 << (lineLength - i - 1);
			} else {
				epsilon = epsilon | 1 << (lineLength - i - 1);
			}
		}

		printf("Answer: %d", gamma * epsilon);

		return 0;
	} else {
		printf("You need to provide a file\n");
		return 1;
	}
}