grasshop.c

#include <stdio.h>
 
#define SIZE 100
 
int R, C, Gr, Gc, Lr, Lc, board[SIZE*SIZE], j, s1, s2, i, r1, r2;
 
int m[8][2] = {{-2, 1}, {-1, 2}, {1, 2}, {2, 1}, {2, -1}, {1, -2}, {-1, -2}, {-2, -1}};
 
 
 
int main() {
 
  while(scanf("%d %d %d %d %d %d", &R, &C, &Gr, &Gc, &Lr, &Lc) == 6) {
 
    for(i = 0; i < SIZE*SIZE; i++) { board[i] = 0; }
 
    board[(Gr-1)*R+Gc-1] = 1;
 
    j = 1;
 
    while (board[(Lr-1)*R+Lc-1] == 0 && j < SIZE) {
      for (s1 = 0; s1 < R; s1++) {
	for (s2 = 0; s2 < C; s2++) {
	  if (board[s1*R+s2] == j) {
	    for(i = 0; i < 8; i++) {
	      r1 = s1+m[i][0];
	      r2 = s2+m[i][1];
 
	      if ((r1 >= 0 && r1 < R && r2 >= 0 && r2 < C) && board[r1*R+r2] == 0) {
		board[r1*R+r2] = j+1;
	      }
	    }
	  }
	}
      }
      j++;
    }
 
    if (board[(Lr-1)*R+Lc-1] > 0)
      printf("%d\n", board[(Lr-1)*R+Lc-1]-1);
    else
      printf("impossible\n");
 
  }
 
  return 0;
 
}