Monday, November 10, 2008

Optimizing Loops

A few ways to optimize loops

Iterating through loops has the following structure in many cases:

for(int k=0; k<someVar.length(); k++)

Check it out, you execute the k=0 command, then you execute the comparison as well as the length method as many times as you have n variables to loop through. Finally you increment k n+1 times. This all leads to a lot of executions. To make it go faster:

int length = someVar.length();
for(int k=0; k<length; k++)

Taking the method call to length() out will increase the loop's speed slightly. However, you're still calling length from the variable table n times. So try it this way instead:

int length = someVar.length();
for(int k=length; k>0; --k)

This will iterate backwards. What that means, is that now you won't be pulling up 2 variables in the comparison. You'll only compare one variable to 0. Although, it isn't necessarily that much more beneficial to call length outside of the loop statement now since your call to length is only executed once.

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