做一个医学项目,其中在病例评分时会用到单源最短路径的算法。单源最短路径的dijkstra算法的思路如下: 2.更新与i直接相邻顶点的dist值。(dist[j]=min{dist[j],dist[i]+cost[i][j]}) 3.知道U=V,停止。 利用php特有的性质,其代码如下: 其中例子为图: 转自: 康瑞的部落 » 单源最短路径php实现
如果存在一条从i到j的最短路径(Vi.....Vk,Vj),Vk是Vj前面的一顶点。那么(Vi...Vk)也必定是从i到k的最短路径。Dijkstra是以最短路径长度递增,逐次生成最短路径的算法。例如:对于源顶点V0,首先选择其直接相邻的顶点中长度最短的顶点Vi,那么当前已知可得从V0到达Vj顶点的最短距离dist[j]=min{dist[j],dist[i]+cost[i][j]}。假设G=
1.从V-U中选择使dist[i]值最小的顶点i,将i加入到U中;
function dijkstra(){ $node_info_arr=array( //结点的邻接表结构 array( 'node_id'=>0, //某个结点的id 'next_node'=>array(4,2,1), 'node_type'=>0, 'cost'=>array(10,30,100) ), array( 'node_id'=>4, //某个结点的id 'next_node'=>array(3), 'node_type'=>1, 'cost'=>array(50) ), array( 'node_id'=>3, //某个结点的id 'next_node'=>array(1), 'node_type'=>1, 'cost'=>array(10) ), array( 'node_id'=>2, //某个结点的id 'next_node'=>array(3,1), 'node_type'=>1, 'cost'=>array(60,60) ), array( 'node_id'=>1, //某个结点的id 'next_node'=>array(), 'node_type'=>2, 'cost'=>array() ) ); $start_node_id=false; //起始结点id $i_cost=array(array()); //两个节点之间的开销 $i_dist=array(); //起始点到各点的最短距离 $b_mark=array(); //是否加入了 foreach($node_info_arr as &$node_info){ if($node_info['node_type']==0){ $start_node_id=$node_info['node_id']; //找到初始节点 } foreach($node_info['next_node'] as $key=>$next_node){ $i_cost[$node_info['node_id']][$next_node]=$node_info['cost'][$key]; } $i_dist[$node_info['node_id']]='INF'; //初始化为无穷大 $b_mark[$node_info['node_id']]=false; //初始化未加入 } if($start_node_id===false){ return '302'; } //计算初始结点到各节点的最短路径 $i_dist[$start_node_id]=0; //初始点到其本身的距离为0 $b_mark[$start_node_id]=true; //初始点加入集合 $current_node_id=$start_node_id; //最近加入的节点id $node_count=count($node_info_arr); for($i=0;$i$val){ if($i_dist[$key]=='INF'||$i_dist[$key]>$i_dist[$current_node_id]+$val){ $i_dist[$key]=$i_dist[$current_node_id]+$val; } } } foreach($i_dist as $key=>$val){ if(!$b_mark[$key]){ if($val!='INF'&&($min=='INF'||$min>$val)){ $min=$val; $candidate_node_id=$key; //候选最近结点id } } } if($min=='INF'){ break; } $current_node_id=$candidate_node_id; $b_mark[$current_node_id]=true; } foreach($i_dist as $key=>$val){ echo $start_node_id.'=>'.$key.':'.$val.'<br>'; }}
运行结果为:
0=>0:0
0=>4:10
0=>3:60
0=>2:30
0=>1:70

What’s still popular is the ease of use, flexibility and a strong ecosystem. 1) Ease of use and simple syntax make it the first choice for beginners. 2) Closely integrated with web development, excellent interaction with HTTP requests and database. 3) The huge ecosystem provides a wealth of tools and libraries. 4) Active community and open source nature adapts them to new needs and technology trends.

PHP and Python are both high-level programming languages that are widely used in web development, data processing and automation tasks. 1.PHP is often used to build dynamic websites and content management systems, while Python is often used to build web frameworks and data science. 2.PHP uses echo to output content, Python uses print. 3. Both support object-oriented programming, but the syntax and keywords are different. 4. PHP supports weak type conversion, while Python is more stringent. 5. PHP performance optimization includes using OPcache and asynchronous programming, while Python uses cProfile and asynchronous programming.

PHP is mainly procedural programming, but also supports object-oriented programming (OOP); Python supports a variety of paradigms, including OOP, functional and procedural programming. PHP is suitable for web development, and Python is suitable for a variety of applications such as data analysis and machine learning.

PHP originated in 1994 and was developed by RasmusLerdorf. It was originally used to track website visitors and gradually evolved into a server-side scripting language and was widely used in web development. Python was developed by Guidovan Rossum in the late 1980s and was first released in 1991. It emphasizes code readability and simplicity, and is suitable for scientific computing, data analysis and other fields.

PHP is suitable for web development and rapid prototyping, and Python is suitable for data science and machine learning. 1.PHP is used for dynamic web development, with simple syntax and suitable for rapid development. 2. Python has concise syntax, is suitable for multiple fields, and has a strong library ecosystem.

PHP remains important in the modernization process because it supports a large number of websites and applications and adapts to development needs through frameworks. 1.PHP7 improves performance and introduces new features. 2. Modern frameworks such as Laravel, Symfony and CodeIgniter simplify development and improve code quality. 3. Performance optimization and best practices further improve application efficiency.

PHPhassignificantlyimpactedwebdevelopmentandextendsbeyondit.1)ItpowersmajorplatformslikeWordPressandexcelsindatabaseinteractions.2)PHP'sadaptabilityallowsittoscaleforlargeapplicationsusingframeworkslikeLaravel.3)Beyondweb,PHPisusedincommand-linescrip

PHP type prompts to improve code quality and readability. 1) Scalar type tips: Since PHP7.0, basic data types are allowed to be specified in function parameters, such as int, float, etc. 2) Return type prompt: Ensure the consistency of the function return value type. 3) Union type prompt: Since PHP8.0, multiple types are allowed to be specified in function parameters or return values. 4) Nullable type prompt: Allows to include null values and handle functions that may return null values.


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