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

  run {
    int n = l(values);
    if (n == 0) ret;
    highs.add(values[0]);
    lows.add(values[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];
      if (value > last)
        highs.set(l(highs)-1, i); // replace last high
      else
        lows.set(l(lows)-1, i); // replace last low
    }
  }
}