public void champ (Grid g) {
   int [][] b = {{2,2,2}, {2,2,2}, {2,2,2}};
   int turn = 1, i, j,   // turn is the turn about to be played, from 1 to 9
       make2 = 0, posWinEX = -1, posWinOH = -1; // these are linear indexes {0, 1, ..., 8}
   for (i=0; i<3; i++)
      for (j=0; j<3; j++) {
         if (g.equals(i, j, g.EX)) {b[i][j] = 3; turn++;}
         else if (g.equals(i, j, g.OH)) {b[i][j] = 5; turn++;}
      }
    // compute posWinEX = the position of a win by EX (-1 if none)
              for (i=0; i<3; i++) {
                  if (b[i][0]*b[i][1]*b[i][2]==18) { posWinEX = 3*i;
                     if (b[i][1]==2) posWinEX=posWinEX+1;
                     else if (b[i][2]==2) posWinEX=posWinEX+2;
                  }
                  if (b[0][i]*b[1][i]*b[2][i]==18) { posWinEX = i;
                     if (b[1][i]==2) posWinEX=posWinEX + 3;
                     else if (b[2][i]==2) posWinEX=posWinEX + 6;
                  }
              }
              if (b[0][0]*b[1][1]*b[2][2]==18) {posWinEX = 0;
                  if (b[1][1]==2) posWinEX=4; else if (b[2][2]==2) posWinEX=8;}
              if (b[0][2]*b[1][1]*b[2][0]==18) {posWinEX = 2;
                  if (b[1][1]==2) posWinEX=4; else if (b[2][0]==2) posWinEX=6;}
    // compute posWinOH = the position of a win by OH (-1 if none)
              for (i=0; i<3; i++) {
                  if (b[i][0]*b[i][1]*b[i][2]==50) { posWinOH = 3*i;
                     if (b[i][1]==2) posWinOH=posWinOH+1;
                     else if (b[i][2]==2) posWinOH=posWinOH+2;
                  }
                  if (b[0][i]*b[1][i]*b[2][i]==50) { posWinOH = i;
                     if (b[1][i]==2) posWinOH=posWinOH + 3;
                     else if (b[2][i]==2) posWinOH=posWinOH + 6;
                  }
              }
              if (b[0][0]*b[1][1]*b[2][2]==50) {posWinOH = 0;
                  if (b[1][1]==2) posWinOH=4; else if (b[2][2]==2) posWinOH=8;}
              if (b[0][2]*b[1][1]*b[2][0]==50) {posWinOH = 2;
                  if (b[1][1]==2) posWinOH=4; else if (b[2][0]==2) posWinOH=6;}
    // try to make 2 in a row, or find a blank square
              if (b[1][1]==2) make2=4; else if (b[0][1]==2) make2=1;
              else if (b[1][0]==2) make2=3; else if (b[1][2]==2) make2=5;
              else if (b[2][1]==2) make2=7; else if (b[0][2]==2) make2=2; 
              else if (b[2][0]==2) make2=6; else if (b[2][2]==2) make2=8;
    
    switch (turn) {
      case 1: g.set(0,0,g.EX); return;
      case 2: if (b[1][1]==2) g.set(1,1,g.OH); else g.set(0,0,g.OH); return;
      case 3: if (b[2][2]==2) g.set(2,2,g.EX); else g.set(1,0,g.EX); return;
      case 4: if (posWinEX!=-1) g.set(posWinEX/3, posWinEX%3, g.OH);  // block
              else g.set(make2/3, make2%3, g.OH); return;
      case 5: if (posWinEX!=-1) g.set(posWinEX/3, posWinEX%3, g.EX);       // win
              else if (posWinOH!=-1) g.set(posWinOH/3, posWinOH%3, g.EX);  // block
              // try for a fork
              else if (b[2][0]==2) g.set(2, 0, g.EX); else g.set(0, 2, g.EX); return;
      case 6: case 8: if (posWinOH!=-1) g.set(posWinOH/3, posWinOH%3, g.OH);  // win
              else if (posWinEX!=-1) g.set(posWinEX/3, posWinEX%3, g.OH);     // block
              else g.set(make2/3, make2%3, g.OH); return;
      case 7: case 9: if (posWinEX!=-1) g.set(posWinEX/3, posWinEX%3, g.EX);  // win
              else if (posWinOH!=-1) g.set(posWinOH/3, posWinOH%3, g.EX);     // block
              else g.set(make2/3, make2%3, g.EX); return; 
   }
  }