I use the multiset initially with the similar method. However, I had a memory limit exist. After, I saw the discussion, then I change the container to priority_queue.
Then I am able to solve the quetion. I just wonder, why with the similar algorithm, the memory usage is different? 1 396 KB vs 972 KB.

The memory usage of multiset is more than simple array is used then sorted. 1 084 KB

multiset uses Red-Black Tree data structure, so it stores for every element not only it's value (4 bytes), but also addresses of it's parent (4 bytes more), both children (8 bytes) and color (enum, 4 bytes). So, as you can see, it spends 28 bytes for every element versus 4 bytes at priority_queue