sclass MountainsAndValleys {
  double[] values;
  new IntBuffer highs;
  new IntBuffer lows;

  run {
    int n = l(values);
    if (n == 0) ret;
    highs.add(0);
    lows.add(0);
    
    int i = 1;
    while (i < n) {
      // find plateau
      
      var value = values[i];
      int j = i+1;
      while (j < n && values[j] == value) ++j;
      
      // are we going up or down?
      
      var last = values[i-1];
      var list = value > last ? highs : lows;
      
      //if (list.last() == i-1)
      if (values[list.last()] == last)
        list.popLast();
      list.add(i);
      
      i = j;
    }
  }
}