Solution to a logical problem in PHP recursive function

We introduced to you about the return value problem in php recursive function in our previous article, so today we will introduce to you the next logical problem in php recursive function, this problem Many friends will show up, and I will explain it to you today!

First of all, we have to know what a recursive function is. Generally speaking, it means calling your own function.

Now we need to design a piece of code to solve the problem of superposition from 1 to 10.

Code A:

<?php
	//递归函数
	$num=10;
	function add($sum){
		static $tot;
		if($sum>=1){
			$tot+=$sum;
			add(--$sum);
		}else{
			return $tot;
		}
	}
	echo add($num);
?>

Code B:

<?php
	//递归函数
	$num=10;
	function add($sum){
		static $tot;
		if($sum>=1){
			$tot+=$sum;
			return add(--$sum);
		}else{
			return $tot;
		}
	}
	echo add($num);
?>

The desired result cannot be printed in A, but can be achieved in B. The only difference between the A and B codes is the addition of a return in the if.

Let’s start analyzing the entire recursive process. You can go and watch Inception to deepen your understanding: (Take the A code that cannot be implemented as an example)

1. Bring 10 into the function , after the if statement is judged, $tot begins to superimpose.

2. Here comes the key point: reduce the parameter by one and then reintroduce it into the function. (No return value!!!)

3. Then the above process keeps looping until $sum=1, from outside to inside, from 10 to 1, these 10 levels of loops have no return value .

4. When $sum=0, a return value is required.

It's like, in Inception, the protagonist wakes up in the 11th floor of dreams, but the dreams of the previous 10 floors are all in the sleep stage. Do you think this protagonist can wake up? It's obviously impossible. He can only be stuck in the 11th level of dreamland and will never wake up.

The only way for the protagonist to wake up is to wake up from every level of his dream and return to real life. Compared with the A code, the B code requires a return value from the first level until the 11th level. So after the 11th layer woke up, the 10th layer was activated, and then activated layer by layer, and finally woke up smoothly, and the final result was output correctly.

Summary:

Through the above logical problems in the PHP recursive function, many friends may feel the same as what they have encountered. , I hope the above two pieces of code can help you solve your problem!

Related recommendations:

Solution to the problem of return value in php recursive function

Analysis of three ways to implement php recursive function

Examples of using php recursive functions

How to use php recursive functions effectively? Typical examples of php recursive functions

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