**邻接表对于无向图的理解

上次我们写了邻接矩阵对于无向图的理解，这次我们继续，完善邻接表对于无向图的代码。

邻接表中有两种结点结构：1.顶点表结点  2.边表的结点

顶点表：

vertex：存储图中个顶点元素的信息;

fisrtedge：指针域  存储首个边表的结点

边表：

adjvex: 邻接点 顶点表中元素的下标;

next: 指针域  下一个邻接点

无向图：                                                                                                                                  相对应的邻接表：

                                               

#include<iostream>
#include<string>
#define maxSize 10
using namespace std;
//定义边表
struct arcNode {
    int arcNum;  //存储顶点的下标
    arcNode* next;
};

//定义顶点表
struct verNode {
    string vertex;
    arcNode* firstedg;
};

class ALGraph {
public:
    ALGraph();
    ALGraph(string str[], int verNum, int arcNum);
    ~ALGraph();
    void DFStra(int v);
    void BFStra(int v);
private:
    int verNum;
    int arcNum;
    //存放顶点表的数组
    verNode adjlist[maxSize];
    //顶点是否呗访问过
    int visited[maxSize] = { 0 };
};

ALGraph::ALGraph() {
    cout << "默认构造函数!" << endl;
}
ALGraph::ALGraph(string str[], int verNum, int arcNum) {
    //图中顶点的赋值
    this->verNum = verNum;
    for (int i = 0; i < this->verNum; i++) {
        adjlist[i].vertex = str[i];
        adjlist[i].firstedg = NULL;
    }
    this->arcNum = arcNum;
    for (int k = 0; k < this->arcNum; k++) {
        int i = 0;
        int j = 0;
        cout << "请输入边依附的顶点下标序号: ";
        cin >> i >> j;
        //单链表头插法  顶点表与边是双向的 即邻接矩阵的数组 arc[i][j]==arc[j][i];
        arcNode* s = new arcNode;
        s->arcNum = j;
        s->next = adjlist[i].firstedg;
        adjlist[i].firstedg= s;

        arcNode* p = new arcNode;
        p->arcNum = i;
        p->next = adjlist[j].firstedg;
        adjlist[j].firstedg = p;
    }
}
ALGraph::~ALGraph() {
    for (int i = 0; i < verNum; i++) {    
        if (adjlist[i].firstedg != NULL) {
            arcNode* p = adjlist[i].firstedg;
            adjlist[i].firstedg = adjlist[i].firstedg->next;
            delete p;
            p = NULL;   //上完厕所洗手
        }
     }
}
void ALGraph::DFStra(int v) {
    cout << adjlist[v].vertex;
    visited[v] = 1;
    arcNode* p = adjlist[v].firstedg;
    while (p != NULL) {
        if (visited[p->arcNum] == 0)
            DFStra(p->arcNum);
        p = p->next;
    }
}
void ALGraph::BFStra(int v) {
    //定义栈并初始化
    int Queue[maxSize];
    int front = -1;
    int rear = -1;
    cout << adjlist[v].vertex;
    visited[v] = 1;
    Queue[++rear] = v;
    while (front != rear) {
        v = Queue[++front];
        arcNode* p = adjlist[v].firstedg;
        //广度
        while (p != NULL) {
            if (visited[p->arcNum] == 0){
                cout << adjlist[p->arcNum].vertex;
                visited[p->arcNum] = 1;
                Queue[++rear] = p->arcNum;
            }
            p = p->next;
        }
    }
}

int main() {
    string str[4] = { "v0","v1","v2","v3" };
    ALGraph myALGraph(str,4,4);
    //myALGraph.DFStra(1);
    //myALGraph.BFStra(1);
    return 0;
}