main.c

#include <stdio.h>
#include <stdlib.h>
 
int sachovnice[101* 101];
int fronta[101*101];
int fronta_f, fronta_c;
int startx, starty;
int cilx, cily;
 
int w, h;
 
int push(int p)
{
  fronta[fronta_f + fronta_c] = p;  
  fronta_c++;
  return 0;   
}
 
int pop()
{
    int rtn;
    if (fronta_c == 0)
      return -1;
    rtn = fronta[fronta_f];
    fronta_f++;
    fronta_c--;
    return rtn;
}
 
int expand(int x, int y, int t)
{
    if (x <= 0 || y <= 0 || x > w || y > h)    
      return 0;
 
    if (sachovnice[x + y * 101] != -1)
      return 0;
 
    push(x + y * 101);
    sachovnice[x + y * 101] = t;
    return 1;
}
 
int init()
{
    memset(sachovnice, 255, 101 * 101 * sizeof(int));
    fronta_f = 0;
    fronta_c = 0;
    expand(startx, starty, 0);
    return 0;
}
 
int main(int argc, char *argv[])
{
    int ex, ey;
  	int v;
  	int done;
 
  	while (scanf("%d %d %d %d %d %d", &w, &h, &startx, &starty, &cilx, &cily) == 6)
  	{
          init();
 
          done = 0;
          do
          {
                 v = pop();
                 if (v == -1)
                 {
                       printf("impossible\n");
                       done = 1;
                 }
                 else
                 {
                     if (v == cily * 101 + cilx)
                     {
                           printf("%d\n", sachovnice[v]);
                           done = 1;
                     }
                     else
                     {
                         ex = v % 101;
                         ey = v / 101;
                         expand(ex + 1, ey + 2, sachovnice[v] + 1);
                         expand(ex - 1, ey + 2, sachovnice[v] + 1);
                         expand(ex + 1, ey - 2, sachovnice[v] + 1);
                         expand(ex - 1, ey - 2, sachovnice[v] + 1);
                         expand(ex + 2, ey + 1, sachovnice[v] + 1);
                         expand(ex - 2, ey + 1, sachovnice[v] + 1);
                         expand(ex + 2, ey - 1, sachovnice[v] + 1);
                         expand(ex - 2, ey - 1, sachovnice[v] + 1);                                                                                                                                                                               
                     }
                 }
          }while(!done);
    }
 
    return 0;
}