knight.c

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

int sgn(int x) {
        return (x >= 0 ? 1 : -1);
}

int main(int argc, char * argv[]) {
        if(argc != 3) {
                printf("ERROR: Supply X and Y target position!\n");
                return -3;
        }
        int X = (int)atoi(argv[1]);
        int Y = (int)atoi(argv[2]);
        printf("Targets: X = %d and Y = %d\n", X, Y);
        int cx, cy = 0;
        int dx, dy, mx, my;
        int moves = 0;

        while(moves < 100000) {
                moves++;
                printf("Position: %d\t%d\n", cx, cy);
                dx = X - cx;
                dy = Y - cy;
                mx = sgn(dx)*(dx % 2 < dy % 2? 2 : 1);
                my = sgn(dy)*(abs(mx) == 2? 1 : 2);
                // Pequena gambiarra. 
                if((abs(dx) == 2 && abs(dy) == 1) || (abs(dx) == 1 && abs(dy) == 2)) {
                        mx = dx;
                        my = dy;
                }
                cx = cx + mx;
                cy = cy + my;
                if(cx == X && cy == Y) {
                        printf("Got there in %d moves\n", moves);
                        return 1;
                }
        }
        printf("Did not succeed...\n");
        return -2;
}