Instead of doing $$$ok[ check.fi ][ check.se ] = 1;$$$ after you pop it from the queue, do it while pushing into the queue. Right now your queue can hold many duplicates of some cell $$$(x,y)$$$. When you push the first instance of $$$(x,y)$$$, you should immediately change the ok status to 1 so that no duplicates of $$$(x,y)$$$ enters the queue.