Hunter algorithms-non-recursion optimization for the evaluation of the Fibonacci series

First code

Class test {public static void main (string ARGs []) {int n = 45; long time1 = now (); system. out. print ("Maid (" + N + ") =" + maid (n); system. out. println ("cost:" + (now ()-time1); time1 = now (); system. out. print ("Maid (" + N + ") =" + maid (n); system. out. println ("cost:" + (now ()-time1);} public static long now () {return system. currenttimemillis ();} public static long maid (int n) {If (n = 1) return 1; if (n = 2) return 1; return maid (n-1) + maid (n-2);} public static long maid (int n) {long num1 = 1; long num2 = 1; if (n = 1 | n = 2) {return 1 ;}long numn = 0; For (INT I = 3; I <= N; I ++) {numn = num1 + num2; num1 = num2; num2 = numn ;}return numn ;}}

Execution result:

Analysis:

The implementation of Fibonacci is based on recursion and there will be many repeated computations. Every computation is a new kind of computation, and the previous computation results are not fully utilized, resulting in a serious waste.

The implementation of fibonacci2 is based on dynamic planning, with bottom-up and full use of the previous computing results. The performance varies greatly.