function allDifferent(a, b, c, d) {
  var count = 0;
  var marks = new Array(false, false, false, false, false, false, false);
  marks[a] = true;
  marks[b] = true;
  marks[c] = true;
  marks[d] = true;

  for (var i=0; i<marks.length; i++) {
    if (marks[i]) {
      count++;
    }
  }

  return (count == 4) ? true : false;
}



function cardMember(needle, haystack) {
  for (var i=0; i<haystack.length; i++) {
    if (needle.id == haystack[i].id) {
      return true;
    }
  }
  return false;
}



function mostExpensive(cards) {
  var i, selected;
  for (i=0; i<cards.length; i++) {
    if (i == 0) {
      selected = cards[i];
    } else if (cards[i].cost > selected.cost) {
      selected = cards[i];
    }
  }
  return selected;
}



function costCompareFunction(a, b) {
  if (b.cost < a.cost) {
    return -1;
  }  else if (b.cost > a.cost) {
    return 1;
  } else {
    return 0;
  }
}



function history(txt) {
  document.getElementById("history").innerHTML = txt + "<br>" + document.getElementById("history").innerHTML;
}