// lists is an array of length K of sorted lists
var next = new Array(k);
var h = new Heap(); // h is sorted on the "value" key of each object you put in
var result = new Array();

for(var i = 0; i < lists.length; i++) {
  h.insert({value: lists[i][0], list: i});
  next[i] = 1;
}

while(!h.empty()) {
  var p = h.extractMin();
  result.append(p.value);
  if(next[p.list] < lists[p.list].length) {
    h.insert({value: lists[i][next[i]], list: i});
    next[p.list]++;
  }
}