fcn qselect(list,nth){	// in place quick select
   fcn(list,left,right,nth){
      if (left==right) return(list[left]);
      pivotIndex:=(left+right)/2; // or median of first,middle,last

      	// partition
      pivot:=list[pivotIndex];
      list.swap(pivotIndex,right);	// move pivot to end
      pivotIndex := left;
      i:=left; do(right-left){	// foreach i in ([left..right-1])
	 if (list[i] < pivot){
	    list.swap(i,pivotIndex);
	    pivotIndex += 1;
	 }
	 i += 1;
      }
      list.swap(pivotIndex,right);	// move pivot to final place

      if (nth==pivotIndex) return(list[nth]);
      if (nth<pivotIndex)  return(self.fcn(list,left,pivotIndex-1,nth));
      return(self.fcn(list,pivotIndex+1,right,nth));
   }(list.copy(),0,list.len()-1,nth);
}