zoukankan      html  css  js  c++  java
  • poj1523--SPF(割点)

    SPF
    Time Limit: 1000MS   Memory Limit: 10000K
    Total Submissions: 7389   Accepted: 3353

    Description

    Consider the two networks shown below. Assuming that data moves around these networks only between directly connected nodes on a peer-to-peer basis, a failure of a single node, 3, in the network on the left would prevent some of the still available nodes from communicating with each other. Nodes 1 and 2 could still communicate with each other as could nodes 4 and 5, but communication between any other pairs of nodes would no longer be possible. 

    Node 3 is therefore a Single Point of Failure (SPF) for this network. Strictly, an SPF will be defined as any node that, if unavailable, would prevent at least one pair of available nodes from being able to communicate on what was previously a fully connected network. Note that the network on the right has no such node; there is no SPF in the network. At least two machines must fail before there are any pairs of available nodes which cannot communicate. 

    Input

    The input will contain the description of several networks. A network description will consist of pairs of integers, one pair per line, that identify connected nodes. Ordering of the pairs is irrelevant; 1 2 and 2 1 specify the same connection. All node numbers will range from 1 to 1000. A line containing a single zero ends the list of connected nodes. An empty network description flags the end of the input. Blank lines in the input file should be ignored.

    Output

    For each network in the input, you will output its number in the file, followed by a list of any SPF nodes that exist. 

    The first network in the file should be identified as "Network #1", the second as "Network #2", etc. For each SPF node, output a line, formatted as shown in the examples below, that identifies the node and the number of fully connected subnets that remain when that node fails. If the network has no SPF nodes, simply output the text "No SPF nodes" instead of a list of SPF nodes.

    Sample Input

    1 2
    5 4
    3 1
    3 2
    3 4
    3 5
    0
    
    1 2
    2 3
    3 4
    4 5
    5 1
    0
    
    1 2
    2 3
    3 4
    4 6
    6 3
    2 5
    5 1
    0
    
    0

    Sample Output

    Network #1
      SPF node 3 leaves 2 subnets
    
    Network #2
      No SPF nodes
    
    Network #3
      SPF node 2 leaves 2 subnets
      SPF node 3 leaves 2 subnets

    Source

     
    #include <cstdio>
    #include <cstring>
    #include <iostream>
    using namespace std;
    const int N = 1001;
    struct Edge
    {
        int from, to, next;
    }E[N*N/2];
    int head[N], num[N], pre[N], lowlink[N];
    int cnt, dfs_clock, root;
    bool iscut[N];
    
    void AddEdge(int u, int v)
    {
        Edge e;
        e={u, v, head[u]};
        E[cnt] = e;
        head[u] = cnt++;
      /*  e={v, u, head[v]};
        E[cnt] = e;
        head[v] = cnt++;*/
        u = u ^ v; v = u ^ v; u = u ^ v;
        e={u, v, head[u]};
        E[cnt] = e;
        head[u] = cnt++;
    
    }
    void dfs(int u, int fa)
    {
        lowlink[u]=pre[u]=++dfs_clock;
        int child = 0;
        for(int i = head[u]; i != -1; i = E[i].next)
        {
            int v = E[i].to;
            if(!pre[v])
            {
                child++;
                dfs(v, u);
                lowlink[u]=min(lowlink[u], lowlink[v]);
                if((u == root && child > 1) || (u != root && pre[u] <= lowlink[v]))
                {
                    num[u]++;
                }
            }
            else if(v !=  fa){
                lowlink[u]=min(lowlink[u], pre[v]);
            }
        }
    }
    int Q = 1;
    void Solve()
    {
        memset(pre, 0, sizeof(pre));
        memset(num, 0, sizeof(num));
        dfs_clock = 0;
    
        for(int i = 1; i <= 1000; i++)
        {
            if(!pre[i]&&head[i] != -1)
            {
                root = i;
                dfs(i, -1);
            }
        }
        printf("Network #%d
    ", Q++);
        bool flag = false;
        for(int i = 1; i <= 1000; i++)
        {
            if(num[i])
            {
                printf("  SPF node %d leaves %d subnets
    ", i, num[i]+1);
                flag = true;
            }
        }
        if(!flag)
            printf("  No SPF nodes");
    }
    int main()
    {
        int a, b;
        while(scanf("%d", &a) != EOF, a)
        {
            memset(head, -1, sizeof(head));
            cnt = 0;
            scanf("%d", &b);
            AddEdge(a, b);
            while(scanf("%d", &a), a)
            {
                scanf("%d", &b);
                AddEdge(a, b);
            }
            Solve();
        }
        return 0;
    }
  • 相关阅读:
    c++11 内存模型解读
    无锁队列的实现
    c++中的原子操作
    还是说Memory Model,gcc的__sync_synchronize真是太坑爹了
    对于Linux平台下C语言开发中__sync_函数的认识
    理解 Memory barrier
    pthread_barrier_init,pthread_barrier_wait简介
    explicit构造函数的作用
    droofs
    27.
  • 原文地址:https://www.cnblogs.com/soTired/p/5117189.html
Copyright © 2011-2022 走看看