2647 Reward

http://acm.hdu.edu.cn/showproblem.php?pid=2647  Reward

使用拓扑排序判断有无环

 

#include<stdio.h>
#include<stdlib.h>
#define N 10005
struct arc_node{
    int adjvex;
    struct arc_node *next;
};
struct vex_node{
    int indegree;
    int num;
    struct arc_node *first_arc;
};
struct vex_node vertex[N];
int queue[N];

int init(int n)
{
    int i;
    for (i = 1; i <= n; i++)
    {
        vertex[i].indegree = 0;
        vertex[i].num = 0;
        vertex[i].first_arc = NULL;
    }
    return 1;
}

int calc(int n)
{
    int begin, end;
    int i, v;
    struct arc_node *p;
    int flag;

    begin = 0;
    end = 0;
    for (i = 1; i <= n; i++)
    {
        if (vertex[i].indegree == 0)
        {
            queue[end++] = i;   //每个顶点最多入队一次
        }
    }
    while (begin < end)
    {
        v = queue[begin++];
        p = vertex[v].first_arc;
        while (p)
        {
            vertex[p->adjvex].indegree--;
            if (vertex[p->adjvex].indegree == 0)   //判断入度是否为0，为0就入队
                queue[end++] = p->adjvex;

            if (vertex[p->adjvex].num < vertex[v].num + 1)
                vertex[p->adjvex].num = vertex[v].num + 1;

            p = p->next;
        }
    }

    flag = 0;
    for (i = 1; i <= n; i++)
    {
        if (vertex[i].indegree != 0)
            flag = 1;  //flag等于1表示有环
    }
    return flag;
}


void main()
{
    int m, n;
    int a, b;
    struct arc_node *p;
    int sum;
    int i, tag;

  // freopen("input.txt", "r", stdin);
    while (scanf("%d%d", &n, &m) != EOF)
    {
        init(n);
        for (i = 0; i < m; i++)
        {
            scanf("%d%d", &a, &b);
            p = vertex[b].first_arc;
            tag = 0;
            while (p)
            {
                if (p->adjvex == a)
                {
                    tag = 1;
                    break;
                }
                p = p->next;
            }
            if (tag == 1)
                continue;

            p = (struct arc_node *)malloc(sizeof(struct arc_node));
            if (!p)
                exit(0);
            p->adjvex = a;
            p->next = vertex[b].first_arc;
            vertex[b].first_arc = p;
            vertex[a].indegree++;
        }

        if (calc(n) == 1)
        {
            printf("%d\n", -1);
        }
        else
        {
            sum = n * 888;
            for (i = 1; i <= n; i++)
            {
                sum +=vertex[i].num;
            }
            printf("%d\n", sum);
        }
    }
}