POJ 1511 Invitation Cards （最短路spfa）

Invitation Cards

题目链接：

http://acm.hust.edu.cn/vjudge/contest/122685#problem/J

Description

In the age of television, not many people attend theater performances. Antique Comedians of Malidinesia are aware of this fact. They want to propagate theater and, most of all, Antique Comedies. They have printed invitation cards with all the necessary information and with the programme. A lot of students were hired to distribute these invitations among the people. Each student volunteer has assigned exactly one bus stop and he or she stays there the whole day and gives invitation to people travelling by bus. A special course was taken where students learned how to influence people and what is the difference between influencing and robbery.
The transport system is very special: all lines are unidirectional and connect exactly two stops. Buses leave the originating stop with passangers each half an hour. After reaching the destination stop they return empty to the originating stop, where they wait until the next full half an hour, e.g. X:00 or X:30, where 'X' denotes the hour. The fee for transport between two stops is given by special tables and is payable on the spot. The lines are planned in such a way, that each round trip (i.e. a journey starting and finishing at the same stop) passes through a Central Checkpoint Stop (CCS) where each passenger has to pass a thorough check including body scan.
All the ACM student members leave the CCS each morning. Each volunteer is to move to one predetermined stop to invite passengers. There are as many volunteers as stops. At the end of the day, all students travel back to CCS. You are to write a computer program that helps ACM to minimize the amount of money to pay every day for the transport of their employees.

Input

The input consists of N cases. The first line of the input contains only positive integer N. Then follow the cases. Each case begins with a line containing exactly two integers P and Q, 1

Output

For each case, print one line containing the minimum amount of money to be paid each day by ACM for the travel costs of its volunteers.

Sample Input

2
2 2
1 2 13
2 1 33
4 6
1 2 10
2 1 60
1 3 20
3 4 10
2 4 5
4 1 50

Sample Output

46
210

Hint

##题意：

又是求所有点到#1的往返路径和的最小值.


##题解：

跟[POJ3268](http://www.cnblogs.com/Sunshine-tcf/p/5751314.html)的区别在于这个题的数据更大.
所以这里只能用spfa来求.
正反各跑一遍spfa即可. 注意细节.
这里为方便写了两个spfa函数，也可以在一个函数里分别处理正向边和方向边.


##代码：
``` cpp
#include
#include
#include
#include
#include
#include
#include
#include
#include
#define LL long long
#define eps 1e-8
#define maxn 1000100
#define inf 0x3f3f3f3f3f3f3f3f
#define IN freopen("in.txt","r",stdin);
using namespace std;

int m,n,k;

LL edges, u[maxn], v[maxn], w[maxn];

LL first[maxn], next[maxn];

LL dis[maxn];

LL edges2, u2[maxn], v2[maxn], w2[maxn];

LL first2[maxn], next2[maxn];

LL dis2[maxn];

void add_edge(LL s, LL t, LL val) {

u[edges] = s; v[edges] = t; w[edges] = val;

next[edges] = first[s];

first[s] = edges++;

}

void add_edge2(LL s, LL t, LL val) {

u2[edges2] = s; v2[edges2] = t; w2[edges2] = val;

next2[edges2] = first2[s];

first2[s] = edges2++;

}

queue q;

bool inq[maxn];

void spfa(int s) {

memset(inq, 0, sizeof(inq));

for(int i=1; i<=n; i++) dis[i] = inf; dis[s] = 0;

while(!q.empty()) q.pop();

q.push(s);

while(!q.empty()) {
    int p = q.front(); q.pop();
    inq[p] = 0;
    for(int e=first[p]; e!=-1; e=next[e]) if(dis[v[e]] > dis[p]+w[e]){
        dis[v[e]] = dis[p] + w[e];
        if(!inq[v[e]]) {
            q.push(v[e]);
            inq[v[e]] = 1;
        }
    }
}

}

void spfa2(int s) {

memset(inq, 0, sizeof(inq));

for(int i=1; i<=n; i++) dis2[i] = inf; dis2[s] = 0;

while(!q.empty()) q.pop();

q.push(s);

while(!q.empty()) {
    int p = q.front(); q.pop();
    inq[p] = 0;
    for(int e=first2[p]; e!=-1; e=next2[e]) if(dis2[v2[e]] > dis2[p]+w2[e]){
        dis2[v2[e]] = dis2[p] + w2[e];
        if(!inq[v2[e]]) {
            q.push(v2[e]);
            inq[v2[e]] = 1;
        }
    }
}

}

int main(int argc, char const *argv[])

{

//IN;

int t; cin >> t;
while(t--)
{
    cin >> n >> m;
    memset(first, -1, sizeof(first)); edges = 0;
    memset(first2, -1, sizeof(first2)); edges2 = 0;
    while(m--){
        LL u,v,w; scanf("%lld %lld %lld",&u,&v,&w);
        add_edge(u,v,w);
        add_edge2(v,u,w);
    }

    spfa(1);
    spfa2(1);

    LL ans = 0;
    for(int i=2; i<=n; i++)
        ans += dis[i]+dis2[i];

    printf("%lld\n", ans);
}

return 0;

}