void DeleteVertex(ALGraph *G) { int i, j; printf("请输入要删除的顶点下标："); scanf("%d", &i);

首先，这个函数的目的是删除一个顶点及其相关的边。下面是代码的完整实现：

void DeleteVertex(ALGraph *G) {
    int i, j;
    printf("请输入要删除的顶点下标：");
    scanf("%d", &i);

    if (i < 0 || i >= G->vexnum) {
        printf("输入的顶点下标不合法！\n");
        return;
    }

    // 删除该顶点的出边
    ArcNode *p = G->vertices[i].firstarc;
    while (p) {
        ArcNode *q = p->nextarc;
        int k = p->adjvex;
        // 删除入边
        ArcNode *r = G->vertices[k].firstarc;
        ArcNode *s = NULL;
        while (r && r->adjvex != i) {
            s = r;
            r = r->nextarc;
        }
        if (r && s) {
            s->nextarc = r->nextarc;
            free(r);
        } else if (r) {
            G->vertices[k].firstarc = r->nextarc;
            free(r);
        }
        free(p);
        p = q;
        G->arcnum--;
    }
    G->vertices[i].firstarc = NULL;

    // 删除该顶点的入边
    for (j = 0; j < G->vexnum; j++) {
        if (j == i) continue;
        p = G->vertices[j].firstarc;
        ArcNode *s = NULL;
        while (p && p->adjvex != i) {
            s = p;
            p = p->nextarc;
        }
        if (p && s) {
            s->nextarc = p->nextarc;
            free(p);
            G->arcnum--;
        } else if (p) {
            G->vertices[j].firstarc = p->nextarc;
            free(p);
            G->arcnum--;
        }
    }

    // 删除该顶点
    for (j = i; j < G->vexnum - 1; j++) {
        G->vertices[j] = G->vertices[j+1];
    }
    G->vexnum--;

    printf("删除顶点成功！\n");
}

首先，输入要删除的顶点下标，检查输入是否合法。然后遍历该顶点的出边，对于每一条出边，找到其指向的顶点，删除该顶点到当前顶点的入边，最后删除该出边。接着遍历整张图的每个顶点，删除指向该顶点的所有入边。最后删除该顶点。