PHP Fabonacci数列

 1 <?php
 2     #Fibonacci数列问题
 3     #f(1) = 1
 4     #f(n) = f(n - 1) + f(n - 2)
 5     #求f(n)
 6 
 7     #递归方法
 8     function fibonacci($n) {
 9         if ($n == 0) {
10             return 0;
11         }
12 
13         if ($n == 1) {
14             return 1;
15         }
16 
17         return fibonacci($n - 1) + fibonacci($n - 2);
18     }
19 
20     #非递归方法
21     function fibonacci_norec($n) {
22         $a = 0;
23         $b = 1;
24 
25         for ($i = 2; $i <= $n; $i++) {
26             $c = $a + $b;
27             $a = $b;
28             $b = $c;
29         }
30 
31         return $c;
32     }
33 
34     echo fibonacci(10);
35     echo "<br>";
36     echo fibonacci_norecr(10);
37 ?>