In a competition, four different functions are observed. All the functions use a single for$-$loop and within the for$-$loop, same set of statements are executed. Consider the following for$-$loop implementations of the four functions:

for $($k $=0$; k $<$ n; k$++)$

for $($k $=0$; k $<$ n; k $+=2)$

for $($k $=1$; k $<$ n; k $*=2)$

for $($k $=$ n; k $>-1$; k$/=2)$

Which function would be the most efficient for runtime?