The examples in this article describe several classic algorithms in PHP. Share it with everyone for your reference, the details are as follows:
5 people stole a bunch of apples and planned to divide the spoils the next day. In the evening, a man walked out and divided all the vegetables and fruits into 5 parts, but there was an extra one. He threw this to the monkey in the tree and hid 1/5 first. Unexpectedly, the other four people also thought the same way. They all divided it into 5 parts like the first person and threw the extra piece to the monkey, stealing 1/5. The next day, everyone divided the spoils, and they also divided it into 5 parts and threw one more to the monkey. The last person got a share. Question: How many apples are there?
for ($i = 1; ; $i++) { if ($i%5 == 1) { //第一个人取五分之一,还剩$t $t = $i - round($i/5) - 1; if($t % 5 == 1) { //第二个人取五分之一,还剩$r $r = $t - round($t/5) - 1; if($r % 5 == 1) { //第三个人取五分之一,还剩$s $s = $r - round($r/5) - 1; if($s % 5 == 1) { //第四个人取五分之一,还剩$x $x = $s - round($s/5) - 1; if($x % 5 == 1) { //第五个人取五分之一,还剩$y $y = $x - round($x/5) - 1; if ($y % 5 == 1) { echo $i; break; } } } } } } }
A group of monkeys line up in a circle and are numbered according to 1, 2,..., n. Then start counting from the 1st one, count to the mth one, kick it out of the circle, start counting from behind it, count to the mth one, kick it out..., and continue in this way until the end. Until there is only one monkey left, that monkey is called the king. Programming is required to simulate this process, input m, n, and output the number of the last king.
function king($n, $m){ $monkeys = range(1, $n); $i=0; $k=$n; while (count($monkeys)>1) { if(($i+1)%$m==0) { unset($monkeys[$i]); } else { array_push($monkeys,$monkeys[$i]); unset($monkeys[$i]); } $i++; } return current($monkeys); } $a = king(5, 2); var_dump($a);
The Tower of Hanoi (also known as the Tower of Hanoi) is an ancient legend in India. Brahma, the god who created the world, left three diamond rods in a temple. The first one was covered with 64 round gold pieces. The largest one was at the bottom, and the others were smaller than the other. They were stacked up one after another. In the temple The monks tirelessly moved them one by one from one stick to another. It was stipulated that the middle stick could be used as a help, but only one could be moved at a time, and the big one could not be placed on top of the small one. . Please run the calculation yourself to find the answer. See the program at the end. Faced with the huge number (the number of times the disk has been moved) 18446744073709551615, it seems that even if the monks spend their entire lives, it is impossible to complete the movement of the gold disk.
Later, this legend evolved into the Tower of Hanoi game:
1. There are three poles A, B and C. There are several plates on pole A
2. When moving one plate at a time, the smaller one can only be stacked on top of the larger one
3. Move all the dishes from pole A to pole C
After research, it was found that the solution to the Tower of Hanoi is very simple, just move the gold pieces in one direction according to the movement rules:
For example, the movement of the third-order Tower of Hanoi: A→C,A→B,C→B,A→C,B→A,B→C,A→C
In addition, the Tower of Hanoi problem is also a classic recursion problem in programming.
function hanoi($n,$x,$y,$z){ if($n==1){ echo 'move disk 1 from '.$x.' to '.$z."\n"; }else{ hanoi($n-1,$x,$z,$y); echo 'move disk '.$n.' from '.$x.' to '.$z."\n"; hanoi($n-1,$y,$x,$z); } } hanoi(3,'A','B','C');
Use PHP to describe bubble sort and quick sort algorithms, the object can be an array
//对数组冒泡排序 function bubble_sort($array){ $count = count($array); if ($count <= 0) return false; for($i=0; $i<$count; $i++){ for($j=$count-1; $j>$i; $j–){ if ($array[$j] < $array[$j-1]){ $tmp = $array[$j]; $array[$j] = $array[$j-1]; $array[$j-1] = $tmp; } } } return $array; } function quick_sort($array) { if (count($array) <= 1) return $array; $key = $array[0]; $left_arr = array(); $right_arr = array(); for ($i=1; $i<count($array); $i++){ if ($array[$i] <= $key) $left_arr[] = $array[$i]; else $right_arr[] = $array[$i]; } $left_arr = quick_sort($left_arr); $right_arr = quick_sort($right_arr); return array_merge($left_arr, array($key), $right_arr); }
Use PHP to describe sequential search and binary search algorithms. Sequential search must consider efficiency. The object can be an ordered array
//使用二分查找数组中某个元素 function bin_sch($array, $low, $high, $k){ if ($low <= $high){ $mid = intval(($low+$high)/2); if ($array[$mid] == $k){ return $mid; }elseif ($k < $array[$mid]){ return bin_sch($array, $low, $mid-1, $k); }else{ return bin_sch($array, $mid+1, $high, $k); } } return -1; }
Write a two-dimensional array sorting algorithm function, which can call PHP built-in functions and has universality
function array_sort($arr, $keys, $order=0) { if (!is_array($arr)) { return false; } $keysvalue = array(); foreach($arr as $key => $val) { $keysvalue[$key] = $val[$keys]; } if($order == 0){ asort($keysvalue); }else { arsort($keysvalue); } reset($keysvalue); foreach($keysvalue as $key => $vals) { $keysort[$key] = $key; } $new_array = array(); foreach($keysort as $key => $val) { $new_array[$key] = $arr[$val]; } return $new_array; }
I hope this article will be helpful to everyone in PHP programming.

Reasons for PHPSession failure include configuration errors, cookie issues, and session expiration. 1. Configuration error: Check and set the correct session.save_path. 2.Cookie problem: Make sure the cookie is set correctly. 3.Session expires: Adjust session.gc_maxlifetime value to extend session time.

Methods to debug session problems in PHP include: 1. Check whether the session is started correctly; 2. Verify the delivery of the session ID; 3. Check the storage and reading of session data; 4. Check the server configuration. By outputting session ID and data, viewing session file content, etc., you can effectively diagnose and solve session-related problems.

Multiple calls to session_start() will result in warning messages and possible data overwrites. 1) PHP will issue a warning, prompting that the session has been started. 2) It may cause unexpected overwriting of session data. 3) Use session_status() to check the session status to avoid repeated calls.

Configuring the session lifecycle in PHP can be achieved by setting session.gc_maxlifetime and session.cookie_lifetime. 1) session.gc_maxlifetime controls the survival time of server-side session data, 2) session.cookie_lifetime controls the life cycle of client cookies. When set to 0, the cookie expires when the browser is closed.

The main advantages of using database storage sessions include persistence, scalability, and security. 1. Persistence: Even if the server restarts, the session data can remain unchanged. 2. Scalability: Applicable to distributed systems, ensuring that session data is synchronized between multiple servers. 3. Security: The database provides encrypted storage to protect sensitive information.

Implementing custom session processing in PHP can be done by implementing the SessionHandlerInterface interface. The specific steps include: 1) Creating a class that implements SessionHandlerInterface, such as CustomSessionHandler; 2) Rewriting methods in the interface (such as open, close, read, write, destroy, gc) to define the life cycle and storage method of session data; 3) Register a custom session processor in a PHP script and start the session. This allows data to be stored in media such as MySQL and Redis to improve performance, security and scalability.

SessionID is a mechanism used in web applications to track user session status. 1. It is a randomly generated string used to maintain user's identity information during multiple interactions between the user and the server. 2. The server generates and sends it to the client through cookies or URL parameters to help identify and associate these requests in multiple requests of the user. 3. Generation usually uses random algorithms to ensure uniqueness and unpredictability. 4. In actual development, in-memory databases such as Redis can be used to store session data to improve performance and security.

Managing sessions in stateless environments such as APIs can be achieved by using JWT or cookies. 1. JWT is suitable for statelessness and scalability, but it is large in size when it comes to big data. 2.Cookies are more traditional and easy to implement, but they need to be configured with caution to ensure security.


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