poj 3255 Roadblocks

http://poj.org/problem?id=3255

第k短路

#include<iostream>
#include<cstdio>
#include<algorithm>
#include<cmath>
#include<queue>
#include<string.h>

using namespace std;

const int N=5001;
const int M=200005;
const int MAX=0x5fffffff;
int head[N];
struct node
{
    int j,k;
    int next;
}side[M];
int dist[N];
bool in[N];
struct tt
{
    int f,g;
    int x;
    bool operator <(const tt a) const
    {
        if(a.f==f)
        return a.g<g;
        return a.f<f;
    }
};
void build(int x,int i)
{
    side[i].next=head[x];
    head[x]=i;
}
void spfa(int n)
{
    queue<int>str;
    memset(in,false,sizeof(false));
    for(int i=1;i<=n;++i)
    dist[i]=MAX;
    dist[n]=0;
    in[n]=true;
    str.push(n);
    while(!str.empty())
    {
        int x=str.front();
        str.pop();
        in[x]=false;
        for(int t=head[x];t!=-1;t=side[t].next)
        {
            if(dist[side[t].j]>dist[x]+side[t].k)
            {
                dist[side[t].j]=dist[x]+side[t].k;
                if(!in[side[t].j])
                {
                   in[side[t].j]=true;
                   str.push(side[t].j);
                }
            }
        }
    }
}
int Astar(int n)
{
    tt k1,k2;
    priority_queue< tt >str;
    k1.f=dist[1];
    k1.g=0;
    k1.x=1;
    str.push(k1);
    int ans=-1;
    while(!str.empty())
    {
        k1=str.top();
        str.pop();
        int x=k1.x;
        if(x==n)
        {
            if(ans==-1)
            {
                ans=k1.g;
            }else
            {//cout<<k1.g<<" "<<ans<<endl;
                if(k1.g>ans)
                return k1.g;
            }
        }
        for(int t=head[x];t!=-1;t=side[t].next)
        {
            k2.x=side[t].j;
            if(dist[k2.x]==MAX)
            continue;
            k2.g=k1.g+side[t].k;
            k2.f=k2.g+dist[k2.x];
            str.push(k2);
        }
    }
    return ans;
}
int main()
{
    //freopen("data.txt","r",stdin);
    int n,m;
    while(scanf("%d %d",&n,&m)!=EOF)
    {
        memset(head,-1,sizeof(head));
        for(int i=0;i<m;++i)
        {
            int x,y,k;
            scanf("%d %d %d",&x,&y,&k);
            side[i].j=y;
            side[i].k=k;
            build(x,i);
            side[i+m].j=x;
            side[i+m].k=k;
            build(y,i+m);
        }
        spfa(n);
        printf("%d\n",Astar(n));
    }
    return 0;
}