3560 Graph’s Cycle Component

http://acm.hdu.edu.cn/showproblem.php?pid=3560

Graph’s Cycle Component   使用广度优先判断是否连通，环的每个顶点的度均为2，判断连通分量的每个顶点的度是否为2来判断是否为环。使用深度优先栈溢出，亦可以使用并查集判断是否连通。

#include<stdio.h>
#include<stdlib.h>
#define N 100005
typedef struct arc_node{
    int adjvex;
    struct arc_node *next;
}arc_node;
typedef struct vex_node{
    int color;
    int degree;  //度
    arc_node *first_arc;
}vex_node;
vex_node vertex[N];
int flag[N];   //标记第i个顶点是否被访问过
int queue[N];   //广度优先所需要的队列

int init(int n)
{
    int i;
    for (i = 0; i < n; i++)
    {
        vertex[i].color = 0;
        vertex[i].degree = 0;
        vertex[i].first_arc = NULL;
    }
    return 1;
}
int insert(int u, int v)
{
    arc_node *p;
    p = (arc_node *)malloc(sizeof(arc_node));
    if (!p)
        exit(0);
    p->adjvex = v;
    p->next = vertex[u].first_arc;
    vertex[u].first_arc = p;
    vertex[u].degree++;

    p = (arc_node *)malloc(sizeof(arc_node));
    if (!p)
        exit(0);
    p->adjvex = u;
    p->next = vertex[v].first_arc;
    vertex[v].first_arc = p;
    vertex[v].degree++;
    return 1;
}
int bfs(int u, int count)
{
    arc_node *p;
    int begin, end;
    int tag;   //tag为0表示该连通分量为环，为1表示该连通分量不是环

    begin = 0;
    end = 0;
    queue[end++] = u;
    flag[u] = 1;
    if (vertex[u].degree == 2)
        tag = 0;
    else
        tag = 1;
    while (begin < end)
    {
        u = queue[begin++];
        p = vertex[u].first_arc;
        while (p)
        {
            if (flag[p->adjvex] == 0)
            {
                queue[end++] = p->adjvex;
                flag[p->adjvex] = 1;
                if (vertex[p->adjvex].degree != 2)
                    tag = 1;   //
            }
            p = p->next;
        }
    }
    if (tag == 0)
        return 1;
    else
        return 0;
}
void main()
{
    int m, n;
    int u, v;
    int i;
    int count, num;
//  freopen("input.txt", "r", stdin);
    while (scanf("%d%d", &n, &m) != EOF && !(n == 0 && m == 0))
    {
        init(n);
        for (i = 0; i < m; i++)
        {
            scanf("%d%d", &u, &v);
            insert(u, v);
        }
        for (i = 0; i < n; i++)
        {
            flag[i] = 0;
        }
        count = 0;  //count用于标记是第几个连通分量
        num = 0;   //num 用于统计环的个数
        for (i = 0; i < n; i++)
        {
            if (flag[i] == 0)
            {

                count++;
                if (bfs(i, count) == 1)
                    num++;
            }
        }
        printf("%d %d\n", count, num);
    }
}