一、目的和要求（需求分析）：

1、掌握邻接表的存储结构以及邻接表的建立和操作。
2、 构造一个无向图的邻接表，要求从键盘输入图的顶点数和图的边数，并显示所构造的邻接表）

基本要求：1. 构造一个无向图的邻接表

2.屏幕输出
实验拓展：
1. 构建有向图的邻接表
2. 判断边是否存在
3. 求顶点的度数

代码

#include<cstdio>
#include<iostream>
#include<iomanip>
using namespace std;
#define MAXVEX 30
typedef char VertexType;
typedef struct ArcNode {
    //表结点
	int adjvex;      /*邻接点序号*/
	VertexType data; /*邻接点信息*/
	struct ArcNode* next;
} ArcNode;

typedef struct VNode {
    //头结点
	VertexType data;   /*结点信息*/
	ArcNode* firsrarc; /*指向下一个边结点*/
}VNode, AdjList[MAXVEX];

typedef struct	ALGraph           //有向与无向图结构
{
    
	int Graph = 0;
	AdjList vertices;
	int vexnum, arcnum;		//图的当前顶点数与弧数
	int in[MAXVEX], out[MAXVEX];//入度与出度记录，无向图仅使用in[]做度记录
}ALGraph;


int LocateVex(ALGraph G, VertexType u)//返回顶点u在图中的位置
{
    
	for (int i = 0; i < G.vexnum; i++) {
    
		if (G.vertices[i].data == u) {
    
			return i;
		}
	}
	return -1;
}

void CreateG(ALGraph& G) {
    //构造图
	cout << "输入数字选择你要构建的图(0无向图|1有向图):" << endl;
	int a; cin >> a;
	G.Graph = a;
	VertexType v1, v2;
	int i, j, k;
	cout << "请输入顶点数和边数：";
	cin >> G.vexnum >> G.arcnum;

	cout << "请输入顶点：" << endl;
	for (i = 0; i <G.vexnum; i++)
	{
    
		cout << "请输入顶点" << i << "的信息:";
		cin >> G.vertices[i].data;
		G.vertices[i].firsrarc = NULL;
	}

	for (int i = 0; i < G.vexnum; i++) {
    
		G.in[i] = 0;
		G.out[i] = 0;
	}

	cout << "请输入边：" << endl;
	for (k = 0; k < G.arcnum; k++)
	{
    
		cout << "请输入弧的信息(弧尾 弧头):";
		cin >> v1 >> v2;
		i = LocateVex(G, v1);
		j = LocateVex(G, v2);

		//插入v1的邻接表。
		ArcNode* arc = new ArcNode;
		arc->adjvex = j;
		arc->next = G.vertices[i].firsrarc;
		G.vertices[i].firsrarc = arc;

		if (G.Graph == 1) {
    //有向图
			G.out[i]++;
			G.in[j]++;
		}
		else {
    
			//插入v2的邻接表
			ArcNode* arc = new ArcNode;
			arc->adjvex = i;
			arc->next = G.vertices[j].firsrarc;
			G.vertices[j].firsrarc = arc;
			G.in[i]++;
			G.in[j]++;
		}
	}
}


void printALGraph(ALGraph G) {
    
	for (int i = 0; i < G.vexnum; i++) {
    
		cout << i << "|" << G.vertices[i].data << " ";
		for (ArcNode* p = G.vertices[i].firsrarc; p; p=p->next) {
    
			cout << "——>" << p->adjvex;
		}
		cout << "——>NULL" << endl;
	}
}

int checkarc(ALGraph G) {
    
	while (1) {
    
		VertexType tail, head ,p;
		fflush(stdin);
		cout << "输入弧的信息(弧尾-弧头):";
		cin >> tail >> head;
		getchar();
		int i = LocateVex(G, tail);
		int j = LocateVex(G, head);
		if (i == -1 || j == -1 || i == j){
    
			cout << "No" << endl;
			continue;
		}

		int flag = 0;
		for (ArcNode* q = G.vertices[i].firsrarc; q; q = q->next) {
    
			if (j == q->adjvex) {
    
				flag = 1;
				break;
			}
		}
		if (flag) cout << "Yes" << endl;
		else cout << "No" << endl;
	}
}

void printdegree(ALGraph G) {
    
	if (G.Graph == 1) {
    
		cout << "  Node  入度 出度  度" << endl;
		for (int i = 0; i < G.vexnum; i++) {
    
			cout << setw(5) << G.vertices[i].data << setw(5) << G.in[i] << setw(5)
				<< G.out[i] << setw(5) << G.in[i] + G.out[i] << endl;
		}
	}
	else {
    
		cout << "  Node   度" << endl;
		for (int i = 0; i < G.vexnum; i++) {
    
			cout << setw(5) << G.vertices[i].data << setw(5) << G.in[i] << endl;
		}
	}
}

int main() {
    
	ALGraph G;
	CreateG(G);
	cout << endl;
	printALGraph(G);
	cout << endl;
	printdegree(G);
	cout << endl;
	checkarc(G);
}