Uva11374 Airport Express

The shortest path.

Run Dijkstra once from the start point and the end point to get the distance from the start point to any point. Enumerate the commercial lines used to find the optimal solution.

When the problem-breaking card is output, it seems that it is more difficult to record the predecessor and output than the algorithm itself.

/*by SilverN*/#include<algorithm>#include<iostream>#include<cstring>#include<cstdio>#include<cmath>#include<vector>#include<queue>using namespace std;const int mxn=2410;int read(){    int x=0,f=1;char ch=getchar();    while(ch<‘0‘ || ch>‘9‘){if(ch==‘-‘)f=-1;ch=getchar();}    while(ch>=‘0‘ && ch<=‘9‘){x=x*10+ch-‘0‘;ch=getchar();}    return x*f;}int n,m,k,S,E;struct exp{    int x,y,w;}ex[mxn];struct edge{    int v,nxt,dis;}e[mxn<<2];int hd[mxn],mct=0;void add_edge(int u,int v,int d){    e[++mct].v=v;e[mct].nxt=hd[u];e[mct].dis=d;hd[u]=mct;    return;}struct node{    int v,d;    bool operator < (const node r) const {return d>r.d;}};priority_queue<node>tp;int pre[mxn],nxt[mxn];int dis[mxn];int mdis[mxn];void Dij1(int st){    while(!tp.empty())tp.pop();    memset(dis,0x3f,sizeof dis);    tp.push((node){st,0});    dis[st]=0;    while(!tp.empty()){        node tmp=tp.top();tp.pop();        if(tmp.d>dis[tmp.v])continue;        int u=tmp.v;        for(int i=hd[u];i;i=e[i].nxt){            int v=e[i].v;            if(dis[v]>dis[u]+e[i].dis){                dis[v]=dis[u]+e[i].dis;                pre[v]=u;                tp.push((node){v,dis[v]});            }        }    }    return;}void Dij2(int st){    while(!tp.empty())tp.pop();    memset(dis,0x3f,sizeof dis);    tp.push((node){st,0});    dis[st]=0;    while(!tp.empty()){        node tmp=tp.top();tp.pop();        if(tmp.d>dis[tmp.v])continue;        int u=tmp.v;        for(int i=hd[u];i;i=e[i].nxt){            int v=e[i].v;            if(dis[v]>dis[u]+e[i].dis){                dis[v]=dis[u]+e[i].dis;                nxt[v]=u;                tp.push((node){v,dis[v]});            }        }    }    return;    }int st[mxn],top=0;void init(){    memset(hd,0,sizeof hd);    memset(pre,0,sizeof pre);    memset(nxt,0,sizeof nxt);    mct=0;top=0;}int main(){    int i,j;    bool flag=0;    while(scanf("%d%d%d%d",&n,&S,&E,&m)!=EOF){        if(flag){            printf("\n");        }        flag=1;        init();        int u,v,w;        for(i=1;i<=m;i++){            u=read();v=read();w=read();            add_edge(u,v,w);            add_edge(v,u,w);        }        k=read();        for(i=1;i<=k;i++){            ex[i].x=read();ex[i].y=read();            ex[i].w=read();        }        Dij1(S);        memcpy(mdis,dis,sizeof dis);        Dij2(E);        int pos1=0,pos2=0,ans=1e9;        for(i=1;i<=n;i++){            if(ans>mdis[i]+dis[i]){                ans=mdis[i]+dis[i];                pos1=i;            }        }        for(i=1;i<=k;i++){            int tmp=mdis[ex[i].x]+dis[ex[i].y]+ex[i].w;            if(ans>tmp){                ans=tmp;pos1=ex[i].x;pos2=ex[i].y;            }            tmp=mdis[ex[i].y]+dis[ex[i].x]+ex[i].w;            if(ans>tmp){                ans=tmp;pos1=ex[i].y;pos2=ex[i].x;            }        }        if(pos1 && !pos2){//            printf("Test1\n");            int tmp=pos1;            while(pre[pos1]){                pos1=pre[pos1];                st[++top]=pos1;            }            while(top)    printf("%d ",st[top--]);            pos1=tmp;            do{                printf("%d",pos1);                if(nxt[pos1])printf(" ");                pos1=nxt[pos1];            }while(pos1);            printf("\nTicket Not Used\n");        }        else{            if(pos1 && pos2){                int tmp=pos1;                while(pre[pos1]){                    pos1=pre[pos1];                    st[++top]=pos1;                }                while(top)    printf("%d ",st[top--]);                pos1=tmp;                printf("%d ",pos1);//                pos2=nxt[pos2];                while(pos2){                    printf("%d",pos2);                    if(nxt[pos2])printf(" ");                    pos2=nxt[pos2];                }                printf("\n%d\n",pos1);            }        }        printf("%d\n",ans);    }    return 0;}

 

Uva11374 Airport Express