PHP 斐波那契数列
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PHP Fibonacci Sequence
提问by Jesse Luke Orange
This php method is suppose to print the Fibonacci sequence up to a specified value using a for loop. I am unsure why it does not work?
这个 php 方法假设使用 for 循环将斐波那契数列打印到指定值。我不确定为什么它不起作用？
<?php
function fib ($n) { // a function called fib, declaire variable n (the sequence number)
for ($n=0;$n<30;$n++) {
if ($n < 3) { return $n; } // if n is smaller than 3 return n (1 or 2)
else { return fib ($n - 1) + fib ($n - 2); }
/* if the number is 3 or above do 2 sums (n-1) and (n-2)
and then add the 2 sums together (n-1)+(n-2)
Example Fibonacci number 4
(4-1)+(4-2) = 5
3 + 2 = 5
*/
}
print $n;
?>
回答by Lee Davis
There is actually a way to calculate a Fibonacci number without iteration by using rounding:
实际上有一种方法可以通过使用舍入来计算无需迭代的斐波那契数：
http://en.wikipedia.org/wiki/Fibonacci_number#Computation_by_rounding
http://en.wikipedia.org/wiki/Fibonacci_number#Computation_by_rounding
function getFib($n)
{
return round(pow((sqrt(5)+1)/2, $n) / sqrt(5));
}
回答by user2669208
Simple function of fibonacci
斐波那契的简单函数
function fibonacci($n,$first = 0,$second = 1)
{
$fib = [$first,$second];
for($i=1;$i<$n;$i++)
{
$fib[] = $fib[$i]+$fib[$i-1];
}
return $fib;
}
echo "<pre>";
print_r(fibonacci(50));
回答by Sathish Jayaraman
In this example, I am using a for loop and limiting the length to 10:
在这个例子中，我使用了一个 for 循环并将长度限制为 10：
$x = 0;
$y = 1;
for($i=0;$i<=10;$i++)
{
$z = $x + $y;
echo $z."<br />";
$x=$y;
$y=$z;
}
Output:
1
2
3
5
8
13
21
34
55
89
144
输出：
1
2
3
5
8
13
21
34
55
89
144
回答by Abdallah Awwad Alkhwaldah
you have 2 sulutions
你有 2 个解决方案
using for loop
使用 for 循环
function fib($n) {
$fib_array = [0, 1];
for ($i = 2; $i < $n; $i++) {
$fib_array[$i] = $fib_array[$i - 1] + $fib_array[$i - 2];
}
return $fib_array;
}
print_r(fib(6));
recursive functions
递归函数
function rec_fib($x) {
if ($n < 2) {
return $n;
}
return fib($n - 1) + fib($n - 2);
}
print_r(rec_fib(6));
回答by Niet the Dark Absol
Your basic understanding of how the language works seems wrong. You're defining a function but never calling it. You are giving a parameter that you then immediately overwrite.
你对语言工作原理的基本理解似乎是错误的。您正在定义一个函数，但从未调用过它。您正在提供一个参数，然后立即覆盖该参数。
Try this:
尝试这个：
$fib = [1,0];
for($i=0; $i<30; $i++) {
$next = array_sum($fib);
array_shift($fib);
array_push($fib,$next);
echo $next.", ";
}
回答by Oswald
You are overwriting the $nyou get as function argument when you let $nto be the loop counter.
$n当你让它$n成为循环计数器时，你正在覆盖你作为函数参数得到的。
Get rid of the for-statement, leave just the body of it.
去掉 -for语句，只留下它的正文。
回答by Petr
I know I am 1 year late, but here is my contribution. There are 2 possible solutions:
我知道我迟到了一年，但这是我的贡献。有两种可能的解决方案：
function fib1($n)
{
return $n < 3 ? 1 : fib1($n - 1) + fib1($n - 2);
}
function fib2($n, $c = 2, $n2 = 0, $n1 = 1)
{
return $c < $n ? fib2($n, $c + 1, $n1, $n1 + $n2) : $n1 + $n2;
}
The first one is more elegant and calculates the result same way as it is defined mathematically. The problem is it is very expensive for big $n.
第一个更优雅，并以与数学定义相同的方式计算结果。问题是大 $n 非常昂贵。
The second one is much faster, but you have to make sure user sets only the first parameter.
第二个要快得多，但您必须确保用户只设置第一个参数。
Execution time:
执行时间处理时间：
$n = 20, fib1 = 0.092s, fib2 = 0.001s
$n = 30, fib1 = 12.2827s, fib2 = 0.001s
$n = 40, fib1 = >500s fib2 = 0.001s
$n = 20, fib1 = 0.092s, fib2 = 0.001s
$n = 30, fib1 = 12.2827s, fib2 = 0.001s
$n = 40, fib1 = >500s fib2 = 0.001s
回答by Josh Woodcock
function fib($m){
$j=0;$k=1;
for($i=0;$i<=$m;$i++){
$l=$k;
$k=$j+$k;
$j=$l;
}
return $k;
}
回答by Guru
回答by Pedro Moreira
A more readable, non-recursive approach:
一种更具可读性的非递归方法：
function fibonacciSequence($max = 13) {
if($max < 1)
return [];
$sequence = [];
$older = 0;
$newer = 1;
do {
$number = $newer + $older;
$sequence[] = $number;
$older = $newer;
$newer = $number;
} while($number < $max);
return $sequence;
}
