%macro HeapInit(size=1000,nchar=20);
do;
	_len = 0;
	_size = &size;
	array _times(&size) _temporary_ ;
	array _kinds(&size) $ &nchar _temporary_;
	drop _size _len;
end;
%mend;
%macro HeapSwapItem(index1, index2);
do;
	_tempN = _times[&index1]; _times[&index1] = _times[&index2]; _times[&index2] = _tempN;
	_tempC = _kinds[&index1]; _kinds[&index1] = _kinds[&index2]; _kinds[&index2]= _tempC;
	drop _tempN _tempC;
end;
%mend;
%macro HeapEmpty;
	(_len=0)
%mend;
%macro HeapCompare(index1, index2);
	(_times[&index1] < _times[&index2])
%mend;
%macro HeapSiftdown(index);
do;
	_parent = &index;
	_done = 0;
	do while (_parent*2 <= _len & ^_done);
		_child = _parent*2;
		if (_child+1 <= _len and %HeapCompare(_child+1,_child)) then
			_child = _child + 1;
		if %HeapCompare(_child,_parent) then do;
			%HeapSwapItem(_child,_parent);
			_parent = _child;
		end;
		else _done = 1;
	end;
	drop _done _parent _child;
end;
%mend;
%macro HeapSiftup(index);
do;
	_child = &index;
	_done = 0;
	do while(_child>1 and ^_done);
		_parent = floor(_child/2);
		if %HeapCompare(_parent,_child) then
			_done = 1;
		else do;
			%HeapSwapItem(_child,_parent);
			_tempN = _child;
			_child = _parent;
			_parent = _tempN;
		end;
	end;
	drop _parent _child _done _tempN;
end;
%mend;	
%macro HeapPush(time, kind);
do;
	if _len >= _size then do;
		put "ERROR: exceeded size of heap. Consider changing size argument to %HeapInit.";
		stop;
	end;
	_len = _len + 1;
	_times[_len] = &time;
	_kinds[_len] = &kind;
	%HeapSiftup(_len);
end;
%mend;
%macro HeapPop;
do;
	_len = _len - 1;
	if (_len>0) then do;
		_times[1] = _times[_len+1];
		_kinds[1] = _kinds[_len+1];
		%HeapSiftdown(1);
	end;
end;
%mend;
%macro HeapPeek;
	time = _times[1];
	kind = _kinds[1];
	put time kind;
%mend;
data _null_;
	%HeapInit;
	%HeapPush(3, "Clear drains");
	%HeapPush(4, "Feed cat");
	%HeapPush(5, "Make tea");
	%HeapPush(1, "Solve RC tasks");
	%HeapPush(2, "Tax return");
	do while(^%HeapEmpty);
		%HeapPeek;
		%HeapPop;
	end;
run;