1160. Network

http://acm.timus.ru/problem.aspx?space=1&num=1160

最短路变形  水题  spfa

代码：

#include<iostream>

#include<cstdio>

#include<cstring>

#include<algorithm>

#include<string>

#include<vector>

#include<map>

#include<queue>

#include<stack>

#include<cmath>

#define LL long long

//#pragma comment(linker, "/STACK:1024000000,1024000000")

using namespace std;



const int INF=0x3f3f3f3f;

const int N=1005;

const int M=30005;

int head[N],I;

struct node

{

    int j,next,v;

}side[M];

int f[N];

void Add(int i,int j,int v)

{

    side[I].j=j;

    side[I].v=v;

    side[I].next=head[i];

    head[i]=I++;

}

int spfa(int s,int n)

{

    int dist[N];

    bool in[N];

    for(int i=1;i<=n;++i)

    dist[i]=INF;

    dist[1]=0;

    memset(in,false,sizeof(in));

    queue<int>qt;

    qt.push(s);

    in[s]=true;

    while(!qt.empty())

    {

        int x=qt.front();qt.pop();

        in[x]=false;

        for(int t=head[x];t!=-1;t=side[t].next)

        {

            int l=side[t].j;

            if(dist[l]>max(dist[x],side[t].v))

            {

                dist[l]=max(dist[x],side[t].v);

                f[l]=x;

                if(!in[l])

                {

                    in[l]=true;

                    qt.push(l);

                }

            }

        }

    }

    int k=0;

    for(int i=1;i<=n;++i)

    k=max(k,dist[i]);

    return k;

}

int main()

{

    //freopen("data.txt","r",stdin);

    int n,m;

    while(scanf("%d %d",&n,&m)!=EOF)

    {

        memset(head,-1,sizeof(head));

        I=0;

        while(m--)

        {

            int a,b,c;

            scanf("%d %d %d",&a,&b,&c);

            Add(a,b,c);

            Add(b,a,c);

        }

        printf("%d\n",spfa(1,n));

        printf("%d\n",n-1);

        for(int i=2;i<=n;++i)

        printf("%d %d\n",f[i],i);

    }

    return 0;

}