References

luku08.tex

@@ -419,7 +419,13 @@ A more difficult problem is
 the \key{3SUM problem} that asks to
 find \emph{three} numbers in the array
 such that their sum is $x$.
-This problem can be solved in $O(n^2)$ time.
+Using the idea of the above algorithm,
+this problem can be solved in $O(n^2)$ time\footnote{For a long time,
+it was thought that solving
+the 3SUM problem more efficiently than in $O(n^2)$ time
+would not be possible.
+However, in 2014, it turned out \cite{gro14}
+that this is not the case.}.
 Can you see how?
 
 \section{Nearest smaller elements}