AoC 2022, day 2 (C)

#include <stdio.h>

// return result of game (loss, draw, win) = (0,1,2)
int game_result( int me, int elf ) {
    // res is basically (me - elf) mod 3, BUT...
    //    +1 to shift to loss as 0 instead of draw
    //    +3 to keep +'ve for mod
    return ((me - elf + 4) % 3);
}

// return score for a move
int move_score( int move ) {
    return (move + 1);
}

// return move to get result against elf
int get_move( int result, int elf ) {
    // res = (me - elf + 1) mod 3 (see game_result())
    //  me = (res + elf - 1) mod 3
    //     = (res + elf + 2) mod 3 (keep +'ve for mod)
    return ((elf + result + 2) % 3);
}

int main() {
    char    line[10];

    int     part1 = 0;
    int     part2 = 0;

    while (fgets( line, sizeof(line), stdin ) != NULL) {
        int elf  = line[0] - 'A';   // convert elf move to [0,2]
        int resp = line[2] - 'X';   // convert response to [0,2]

        // Part 1: take response as move to make
        part1 += 3 * game_result( resp, elf ) + move_score( resp );

        // Part 2: response is result of game desired
        part2 += 3 * resp + move_score( get_move( resp, elf ) );
    }

    printf( "Part 1: %d\n", part1 );
    printf( "Part 2: %d\n", part2 );
}