How to implement breadth and depth first traversal of adjacency matrix graph in PHP (code)

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1. The depth-first traversal of the graph is similar to the pre-order traversal, and the breadth-first traversal of the graph is similar to the level-order traversal of the tree.
2. Deform the graph, divide it hierarchically according to the relationship between vertices and edges, and use queues. To traverse
3. The key point of breadth-first traversal is to use a queue to store all the next-level associated points of the current node, and then perform the breadth-first traversal of the adjacency matrix in sequence:

BFS(G)
for i=0;i<G->numVertexes;i++
visited[i]=false;//检测是否访问过
for i=0;i<G.numVertexes;i++//遍历顶点
if visited[i]==true break;//访问过的断掉
visited[i]=true //当前顶点访问
InQueue(i)      //当前顶点入队列
while(!QueueEmpty()) //当前队列不为空
i=OutQueue() //队列元素出队列
for j=0;j<G->numVertexes;j++ //遍历顶点
if G->arc[i][j]==1 && !visited[j] //当前顶点与其他顶点存在关系并且未被访问
visited[j]=true //标记此顶点
InQueue(j)      //此顶点入队列,会排在后面等前面一层的全遍历完才会遍历这个

Depth-first traversal of DFS:

DFSTravserse G
    for i=0;i<G.xNum;i++
        if !visted[i]
            DFS(G,i)
DFS G,i
    visted[i]=true
    print G.vexs[i]
    if G.arc[i][j]==1 && !visited[j]
        DFS(G,j)

Implementation of physical storage of graph:

Adjacency matrix adjacency linked list cross linked list adjacency multiple table

Storage method of directed graph: cross linked list

Optimization of undirected graph storage: adjacent multiple tables

Traversal of graph:

1. From a certain vertex in the graph Start visiting the remaining vertices in the graph, and make each vertex visited only once

2. You need to mark the visited vertices, set an array visited[n], and set it to 1 after the visit

3. Traverse Order: depth-first traversal and breadth-first traversal

Depth-first traversal DFS:

1. Similar to the right-hand rule of walking in a maze, mark one step and keep going to the right until it is repeated. Return to the previous vertex

2. Start from a certain vertex v to access the vertex with the same path as v, and call recursively

<?php
class Graph{
        public $vertexs;
        public $arc;
        public $num=5;
}
$G=new Graph();
for($i=0;$i<$G->num;$i++){
        $G->vertexs[$i]="V{$i}";
}
$G->arc[1][0]=9;
$G->arc[1][2]=3;
$G->arc[2][0]=2;
$G->arc[2][3]=5;
$G->arc[3][4]=1;
$G->arc[0][4]=6;
//广度优先遍历
function BFS($G){
        $res=array();
        $queue=array();
        for($i=0;$i<$G->num;$i++){
                $visited[$i]=false;
        }   
        for($i=0;$i<$G->num;$i++){
                if($visited[$i]){
                        break;
                }   
                $visited[$i]=true;
                $res[]=$G->vertexs[$i];
                array_push($queue,$i);
                while(!empty($queue)){
                        $v=array_pop($queue);
                        for($j=0;$j<$G->num;$j++){
                                if($G->arc[$v][$j]>0 && !$visited[$j]){
                                        $visited[$j]=true;
                                        $res[]=$G->vertexs[$j];
                                        array_push($queue,$j);
                                }   
                        }   
                }   
        }   
        return $res;
}
//深度优先遍历
function DFS($G,$i){
        static $res;
        static $visited;
        if(!$visited[$i]){
                $visited[$i]=true;
                $res[]=$G->vertexs[$i];
        }
                for($j=0;$j<$G->num;$j++){
                        if($G->arc[$i][$j]>0 && !$visited[$j]){
                                $visited[$j]=true;
                                $res[]=$G->vertexs[$j];
                                DFS($G,$j);
                        }
                }
        return $res;
}
$b=BFS($G);
$d=DFS($G,1);
var_dump($b);
var_dump($d);

array(5) {
  [0]=>
  string(2) "V0"
  [1]=>
  string(2) "V4"
  [2]=>
  string(2) "V1"
  [3]=>
  string(2) "V2"
  [4]=>
  string(2) "V3"
}
array(5) {
  [0]=>
  string(2) "V1"
  [1]=>
  string(2) "V0"
  [2]=>
  string(2) "V4"
  [3]=>
  string(2) "V2"
  [4]=>
  string(2) "V3"
}

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