#include int main(int argc, char *argv[]) { /* The Elves play this game by taking turns arranging the marbles in * a circle according to very particular rules. */ #define MAX_ELVES 1000 static int score[MAX_ELVES] = {0}; int winning_score = 0; int elf, num_elves, winner; #define MAX_MARBLES 100000 static int stock[MAX_MARBLES]; static int circle[MAX_MARBLES]; int circle_size = 0; int current, next, last; if ( argc < 3 || sscanf(argv[1], "%d", &num_elves) != 1 || num_elves > MAX_ELVES || sscanf(argv[2], "%d", &last) != 1 || last >= MAX_MARBLES ) return 1; /* The marbles are numbered starting with 0 and increasing by 1 * until every marble has a number. */ for (int i = 0; i <= last; ++i) { stock[i] = i; } next = 0; /* First, the marble numbered 0 is placed in the circle. * At this point, while it contains only a single marble, it is * still a circle: the marble is both clockwise from itself and * counter-clockwise from itself. This marble is designated the * current marble. */ circle[current = circle_size++] = stock[next++]; /* Then, each Elf takes a turn... */ for (;;) for (elf = 0; elf < num_elves; ++elf) { if (0) { printf("%d: ", elf); for (int i = 0; i < circle_size; ++i) { printf("%s%d%s ", "["+(i!=current), circle[i], "]"+(i!=current)); } putchar('\n'); } /* ...placing the lowest-numbered remaining marble * into the circle between the marbles that are 1 and * 2 marbles clockwise of the current marble. (When * the circle is large enough, this means that there * is one marble between the marble that was just * placed and the current marble.) The marble that * was just placed then becomes the current marble. * * However, if the marble that is about to be placed * has a number which is a multiple of 23, something * entirely different happens. */ if (stock[next] % 23) { current = (current + 2) % circle_size; for (int i = circle_size++; i > current; --i) { circle[i] = circle[i - 1]; } circle[current] = stock[next++]; } else { /* First, the current player keeps the marble * they would have placed, adding it to their * score. */ score[elf] += stock[next++]; /* In addition, the marble 7 marbles counter- * clockwise from the current marble is removed * from the circle and also added to the * current player's score. The marble located * immediately clockwise of the marble that was * removed becomes the new current marble. */ current += circle_size - 7 % circle_size; current %= circle_size; score[elf] += circle[current]; --circle_size; for (int i = current; i < circle_size; ++i) { circle[i] = circle[i + 1]; } /* The goal is to be the player with the highest score... */ if (score[elf] > winning_score) { winning_score = score[winner = elf]; if (0) { printf("%d: %d\n", winner, winning_score); } } } /* ...after the last marble is used up. */ if (next > last) { printf("%d\n", winning_score); return 0; } } }