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#include <err.h>
#include <stdio.h>
#include <stdlib.h>
#include <string.h>
struct coords {
int north;
int east;
};
int
main(void)
{
FILE *fp;
char cl[6];
struct coords waypoint = {1, 10};
struct coords ship = {0, 0};
if (!(fp = fopen("input", "r")))
err(EXIT_FAILURE, "fopen");
while (fgets(cl, sizeof(cl), fp) != NULL) {
switch (cl[0]) {
case 'N':
waypoint.north += atoi(&cl[1]);
break;
case 'E':
waypoint.east += atoi(&cl[1]);
break;
case 'S':
waypoint.north -= atoi(&cl[1]);
break;
case 'W':
waypoint.east -= atoi(&cl[1]);
break;
case 'F':;
unsigned int const val = atoi(&cl[1]);
ship.north += val * waypoint.north;
ship.east += val * waypoint.east;
break;
/* Left and right */
default:;
int direction = atoi(&cl[1]);
/* (x, y) -> (-x, -y) */
if (direction == 180) {
waypoint.north = -waypoint.north;
waypoint.east = -waypoint.east;
break;
}
/* 0 <= direction < 360 */
if (cl[0] == 'R')
direction = -direction + 360;
int const temp = waypoint.east;
if (direction == 90) {
/* (x, y) -> (-y, x) */
waypoint.east = -waypoint.north;
waypoint.north = temp;
} else {
/* (x, y) -> (y, -x) */
waypoint.east = waypoint.north;
waypoint.north = -temp;
}
break;
}
}
fclose(fp);
/* Absolute value */
if (ship.north < 0)
ship.north = -ship.north;
if (ship.east < 0)
ship.east = -ship.east;
printf("%d\n", ship.north + ship.east);
return EXIT_SUCCESS;
}
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