2017多校-10

Two Paths
http://acm.hdu.edu.cn/showproblem.php?pid=6181
次短路（代码上网搜的模板）。。。开始INF=le9一直超时，看到评论区有人讨论，改为le18就过了。。。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cstring>
#include <queue>
#define LL long long
#define MAXN 100005
#define INF 1e18
using namespace std;

struct node
{
    LL v, w, next;
} edge[MAXN * 2];

LL n, m, e, p, q;
LL vis[MAXN], dis[MAXN], disr[MAXN], head[MAXN];

void insert(LL x, LL y, LL w)
{
    edge[e].v = y;
    edge[e].w = w;
    edge[e].next = head[x];
    head[x] = e++;
}

void spfa(LL src, LL d[])
{
    memset(vis, 0, sizeof(vis));
    vis[src] = 1;
    d[src] = 0;
    queue<LL> Q;
    Q.push(src);
    while(!Q.empty())
    {
        p = Q.front();
        Q.pop();
        vis[p] = 0;
        for(LL i = head[p]; i != -1; i = edge[i].next)
        {
            LL v = edge[i].v;
            LL w = edge[i].w;
            if(d[v] > d[p] + w)
            {
                d[v] = d[p] + w;
                if(!vis[v])
                {
                    vis[v] = 1;
                    Q.push(v);
                }
            }
        }
    }
}

int main()
{
    int t;
    scanf("%d",&t);
    while(t--)
    {
        LL a, b,c;
        scanf("%lld%lld", &n, &m);
        e = 0;
        memset(head, -1, sizeof(head));
        memset(dis, 0x3f, sizeof(dis));
        memset(disr, 0x3f, sizeof(dis));
        for(LL i = 0; i < m; i++)
        {
            scanf("%lld%lld%lld", &a, &b, &c);
            insert(a, b, c);
            insert(b, a, c);
        }
        spfa(1, dis);
        spfa(n, disr);
        LL mini = dis[n];
        LL ans = INF;
        for(LL i = 1; i <= n; i++)
        {
            for(LL j = head[i]; j != -1; j = edge[j].next)
            {
                LL v = edge[j].v;
                LL w = edge[j].w;
                if(dis[i] + disr[v] + w > mini && dis[i] + disr[v] + w < ans)
                    ans = dis[i] + disr[v] + w;
            }
        }
        printf("%lld\n",ans);
    }
    return 0;
}