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Fibonacci with dynamic programming
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| /** | |
| @param n calculate fibonacci number of n | |
| */ | |
| function f(a){ | |
| return a < 2 ? //Simple case for first two fibonacci numbers | |
| a : | |
| f[a]||(f[a]=f(a-1)+f(a-2)) //Return value of cache or add value to cache if needed. The function is used as cache. | |
| } |
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| function f(a){return a<2?a:f[a]||(f[a]=f(a-1)+f(a-2))} |
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| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| Version 2, December 2004 | |
| Copyright (C) 2011 YOUR_NAME_HERE <YOUR_URL_HERE> | |
| Everyone is permitted to copy and distribute verbatim or modified | |
| copies of this license document, and changing it is allowed as long | |
| as the name is changed. | |
| DO WHAT THE FUCK YOU WANT TO PUBLIC LICENSE | |
| TERMS AND CONDITIONS FOR COPYING, DISTRIBUTION AND MODIFICATION | |
| 0. You just DO WHAT THE FUCK YOU WANT TO. |
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| { | |
| "name": "fastRecursiveFibonacciWithDynamicProgramming", | |
| "description": "A recursive but fast implementation of Fibonacci using dynamic programming.", | |
| "keywords": [ | |
| "fibonacci", | |
| "recursive", | |
| "fast", | |
| "dynamic", | |
| "programming" | |
| ] | |
| } |
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| <!DOCTYPE html> | |
| <title>Fast recursive Fibonacci</title> | |
| <div>Expected value: <b>190392490709135</b></div> | |
| <div>Actual value: <b id="ret"></b></div> | |
| <script> | |
| // write a small example that shows off the API for your example | |
| // and tests it in one fell swoop. | |
| var myFunction = function f(a){return a<2?a:f[a]||(f[a]=f(a-1)+f(a-2))} | |
| document.getElementById( "ret" ).innerHTML = myFunction(70); | |
| </script> |
But then it's leaking the global scope, which is against rule 3. But I see others doing that.
Em... It wouldn't leak the global scope actually.
For example, the following code will cause "Uncaught ReferenceError: f is not defined",
as Function expressions is not Function declarations.
var a = function f(){};
alert(f);
OK, I see what you did there.
why not use the function as the cache?
function f(a){return f[a]=a<3?1:f[a]||f(a-1)+f(a-2)}
Smart move!
That was indeed a smart move. But it destroyed the case where a is 0. Your code returns 1 for f(0) which is by definition 0.
I committed a tweaked version of yours, which is just two bytes longer.
well, you only need the extra two bytes avoid the unneeded assignment. since it's so cheap, i think it's worth it.
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Try to reuse the original function
function f(n,c){return(c=c||[0,1,1])[n]||(c[n]=f(n-1,c)+f(n-2,c))}