图采用邻接表存储，判断顶点i和顶点j（i！=j)是否有路径

从顶点i开始到顶点j进行一次BFS，遍历过程如果访问到了vj，则判定vi与vj存在路径。

#define MaxSize 10

typedef struct ArcNode{
     
    struct ArcNode* next;
    int adjNum;
}ArcNode;

typedef struct{
     
    ArcNode* firstArc;
    char data;
}VNode;

typedef struct{
     
    VNode adjList[MaxSize];
    int n;
    int e;
}AGraph;

void initAGraph(AGraph* &G){
     
    G->e = 3;
    G->n = 4;
    cout<<"data:"<<endl;
    for (int i = 0; i < G->n; i++) {
     
        cin>>G->adjList[i].data;
        G->adjList[i].firstArc = NULL;
    }
    cout<<"vi,vj"<<endl;
    for (int j = 0; j < G->e; j++) {
     
        int vi,vj;
        cin>>vi>>vj;
        ArcNode* node = new ArcNode();
        node->adjNum = vj;
        node->next = G->adjList[vi].firstArc;
        G->adjList[vi].firstArc = node;
    }
}

int visit[MaxSize];

void ArcVisit(VNode node){
     
    cout<<"current: "<<node.data<<endl;
}

//Judge the path of vi to vj is valid
int ValidPath(AGraph* G,int vi, int vj){
     
    int queue[MaxSize];
    int front = 0,rear = 0;
    ArcNode* node;
    
    //Root gets into queue
    rear = (rear + 1)%MaxSize;
    queue[rear] = vi;
    ArcVisit(G->adjList[vi]);

    //Process current logic
    while (front != rear) {
     
        front = (front + 1)%MaxSize;
        int num = queue[front];
        node = G->adjList[num].firstArc;
        while (node) {
     
            rear = (rear + 1)%MaxSize;
            queue[rear] = node->adjNum;
            if (visit[node->adjNum] == 0) {
     
                ArcVisit(G->adjList[node->adjNum]);
                visit[node->adjNum] = 1;
            }
            node = node->next;
        }
    }
    if (visit[vj] == 1) {
     
        return 1;
    }else{
     
        return 0;
    }
}


int main(int argc, const char * argv[]) {
     
    AGraph* G = new AGraph();
    initAGraph(G);
    int ret = ValidPath(G, 0, 3);
    cout<<"valid:"<<ret<<endl;
    return 0;
}