PHP two ways to achieve the Fibonacci number

2. Use recursive methods.

   // using recursion to find Fibonacci numbers     Public function fb ($n) {  //        if$n <=2) {              return 1;        } Else {            return fb ($n-1) + FB ($n-2);        }    }

3. Use a recursive approach.
   

       //using recursion to find the Fibonacci number     Public functionFB2 ($n){//        if($n<=2){            return1; }        $t 1= 1;$t 2= 1;  for($i= 3;$i<$n;$i++){            $temp=$t 1; $t 1=$t 2; $t 2=$temp+$t 2; }        return $t 1+$t 2; }

   
   Finally, perform a performance analysis.
   Obviously predictable, recursive methods, each layer, will be recursive down two times. About O (2 of the n-th square) and the recursive method is O (n), the actual code is as follows.

   /** Performance tuning. */functionBench_profile ($starttime,$flag= ' '){    $endtime=Explode(‘ ‘,Microtime()); $thistime=$endtime[0]+$endtime[1]-($starttime[0]+$starttime[1]); $thistime=round($thistime, 3); return  $flag." -bench: ".$thistime. "SEC";}//use recursive algorithms.         Ini_set("Max_execution_time", 3600); $s=Explode(‘ ‘,Microtime()); EchoBench_profile ($s)." <br/> "; EchoFB (35);//use recursion time-consuming 40.925 sec each to the previous number about twice times slower       EchoBench_profile ($s)." <br/> "; $s=Explode(‘ ‘,Microtime()); EchoBench_profile ($s)." <br/> "; EchoFB2 (35);//The use of recursive time is extremely short.        EchoBench_profile ($s)." <br/> ";

   Summary: Code performance is a good key that distinguishes programmers from getting started and not getting started.
   Using a recursive algorithm, go to 100thFibonacci numberWhen the machine does not move, and the use of recursive algorithm, almost no time.

PHP two ways to achieve the Fibonacci number