LUOGU P1342 請柬(最短路)

標籤：tchar   解題思路   code   ble   def   set   span   closed   pop   

傳送門

 

解題思路

又是一道語文題，弄清楚題意之後其實就能想出來了，從1跑一遍最短路，把$dis[n]$加入答案。在建個反圖跑一遍最短路，把$dis[n]_$加入最短路就行了。第一遍是去的時候，第二遍是回的時候。

#include<iostream>#include<cstdio>#include<cstring>#include<cmath>#include<queue>using namespace std;const int MAXN = 1000005;typedef long long LL;inline int rd(){    int x=0,f=1;char ch=getchar();    while(!isdigit(ch)) {f=ch==‘-‘?0:1;ch=getchar();}    while(isdigit(ch))  {x=(x<<1)+(x<<3)+ch-‘0‘;ch=getchar();}    return f?x:-x;}int n,m,head[MAXN],cnt;int to[MAXN],nxt[MAXN],val[MAXN];int head_[MAXN],cnt_,val_[MAXN],nxt_[MAXN],to_[MAXN];LL dis[MAXN],ans;bool vis[MAXN];struct Node{    int w,id;    friend bool operator<(const Node A,const Node B){        return A.w>B.w;    }};priority_queue<Node> Q;inline void add(int bg,int ed,int w){    to[++cnt]=ed,val[cnt]=w,nxt[cnt]=head[bg],head[bg]=cnt;}inline void add_(int bg,int ed,int w){    to_[++cnt_]=ed,val_[cnt_]=w,nxt_[cnt_]=head_[bg],head_[bg]=cnt_;}void dijkstra(){    memset(dis,0x3f,sizeof(dis));    Node now;now.id=1;now.w=0;dis[1]=0;Q.push(now);    while(!Q.empty()){        Node zz=Q.top();Q.pop();int x=zz.id;        if(dis[x]!=zz.w || vis[x]) continue;vis[x]=1;        for(register int i=head[x];i;i=nxt[i]){            int u=to[i];            if(dis[u]<=dis[x]+val[i]) continue;            dis[u]=dis[x]+val[i];            now.id=u;now.w=dis[u];Q.push(now);        }    }    for(register int i=2;i<=n;i++) ans+=dis[i];}void dijkstra_(){    memset(vis,false,sizeof(vis));    memset(dis,0x3f,sizeof(dis));    Node now;now.id=1;now.w=0;dis[1]=0;Q.push(now);    while(!Q.empty()){        Node zz=Q.top();Q.pop();int x=zz.id;        if(dis[x]!=zz.w || vis[x]) continue;vis[x]=1;        for(register int i=head_[x];i;i=nxt_[i]){            int u=to_[i];            if(dis[u]<=dis[x]+val_[i]) continue;            dis[u]=dis[x]+val_[i];            now.id=u;now.w=dis[u];Q.push(now);        }    }    for(register int i=2;i<=n;i++) ans+=dis[i];}int main(){    n=rd(),m=rd();int x,y,z;    for(register int i=1;i<=m;i++){        x=rd(),y=rd(),z=rd();        add(x,y,z),add_(y,x,z);    }    dijkstra(),dijkstra_();cout<<ans;    return 0;}

View Code

 

LUOGU P1342 請柬(最短路)