# why there is a gap between the caption of this table and table [duplicate]

why there is a gap between the caption of this table and table?

\begin{table}[!h]
\caption{Total times in second and number of sub-problems of  Algorithm 1,2 and 3}
\label{table2}
\begin{center}
\begin{tabular}{|c|c|c|c|c|}
\hline
Name  &  Algorithm & Cycle & Total time (s) &  \shortstack{ Number of \\ sub-problems} \\
\hline
P1    &  1  & $(1,2,3,4,5)$ & 3.1 &3\\
\hline
P2 &  2 &  (1,15,7,5,12)  & 17 & 11 \\
\hline
P2 &  3 & $(1,15,7,5,12)$  $(2,9,13,14,8)$ & 97& 36  \\
\hline
P3 &  2 & $(1,7,12,16,19,21,6)$, & 15&14\\
\hline
P4 & 2 &   $(11,28,29,38,44,25,20,37)$ &335& 36\\
\hline
P4 & 3 &   \shortstack{ $(11,28,29,38,44,25,20,37)$,\\   $(18,33,34,24,40,36,41,39)$} &  566 & 91\\
\hline
\end{tabular}
\end{center}
\end{table}