Hdu 1827 Summer Holiday

 

大意：听说lcy帮大家预定了新马泰7日游，Wiskey真是高兴的夜不能寐啊，他想着得快点把这消息告诉大家，虽然他手上有所有人的联系方式，但是一个一个联系过去实在太耗时间和电话费了。他知道其他人也有一些别人的联系方式，这样他可以通知其他人，再让其他人帮忙通知一下别人。你能帮Wiskey计算出至少要通知多少人，至少得花多少电话费就能让所有人都被通知到吗？

思路：强连通+缩点，然后统计入度为0的点，然后枚举每个SCC中花费最小的值相加，即cost[belong[i]] = min(cost[belong[i]], money[i]);

CODE：

 

#include<cstdio>
#include<cstring>
#include<cstdlib>
#include<algorithm>
using namespace std;

const int MAXN = 1010;
const int MAXM = 2010;
const int INF = 0x3f3f3f3f;

struct Edge
{
    int v, next;
}edge[MAXM];

int n, m;
int cnt;
int tot, scnt, top, ans;
int first[MAXN], stack[MAXN], ins[MAXN], low[MAXN], dfn[MAXN];
int ind[MAXN], outd[MAXN];
int belong[MAXM];
int money[MAXN], cost[MAXN];

inline void init()
{
    cnt = 0;
    tot = scnt = top = 0;
    ans = 0;
    memset(first, -1, sizeof(first));
    memset(dfn, 0, sizeof(dfn));
    memset(ins, 0, sizeof(ins));
    memset(ind, 0, sizeof(ind));
}

inline void read_graph(int u, int v)
{
    edge[cnt].v = v;
    edge[cnt].next = first[u], first[u] = cnt++;
}

inline void read_graph2()
{
    for(int i = 1; i <= n; i++) scanf("%d", &money[i]);
    while(m--)
    {
        int u, v;
        scanf("%d%d", &u, &v);
        read_graph(u, v);
    }
}

inline void dfs(int u)
{
    int v;
    dfn[u] = low[u] = ++tot;
    ins[u] = 1;
    stack[top++] = u;
    for(int e = first[u]; e != -1; e = edge[e].next)
    {
        v = edge[e].v;
        if(!dfn[v])
        {
            dfs(v);
            low[u] = min(low[u], low[v]);
        }
        else if(ins[v])
        {
            low[u] = min(low[u], dfn[v]);
        }
    }
    if(dfn[u] == low[u])
    {
        scnt++;
        do
        {
            v = stack[--top];
            belong[v] = scnt;
            ins[v] = 0;
        }while(v != u);
    }
}

inline void Tarjan()
{
    for(int v = 1; v <= n; v++) if(!dfn[v])
        dfs(v);
}
 
inline void solve()
{
    Tarjan();
    for(int u = 1; u <= n; u++)
    {
        for(int e = first[u]; e != -1; e = edge[e].next)
        {
            int v = edge[e].v;
            if(belong[u] != belong[v])
            {
                ind[belong[v]]++;
            }
        }
    }
    int SCC = 0;
    for(int i = 1; i <= scnt; i++)
    {
        if(ind[i] == 0) SCC++;
        cost[i] = INF;
    }
    for(int i = 1; i <= n; i++)
    {
        if(ind[belong[i]] == 0)
        {
            cost[belong[i]] = min(cost[belong[i]], money[i]);
        }
    }
    for(int i = 1; i <= scnt; i++) if(cost[i] != INF)
    {
        ans += cost[i];
    }
    printf("%d %d\n", SCC, ans);
}

int main()
{
    while(~scanf("%d%d", &n, &m))
    {
        init();
        read_graph2();
        solve();
    }
    return 0;
}