次短路LuoguP2865

#include<cstdio>
#include<cstring>
#include<queue>
using namespace std;

int n,r,head[1000005],dis1[1000005],dis2[1000005],vis[1000005],cnt;

struct edge{
    int v,w,next;
}e[1000005];

struct node{
    int dis,u;
    bool operator<(const node &x)const{return x.dis<dis;}
};

inline void add(int u,int v,int w){
    e[++cnt].v=v;
    e[cnt].w=w;
    e[cnt].next=head[u];
    head[u]=cnt;
}

inline void dijkstra(){
    priority_queue<node> q;
    q.push((node){0,1});
    dis1[1]=0;
    while(!q.empty()){
        int x=q.top().u;
        int dis=q.top().dis;//必须有 
        q.pop();
        for(int i=head[x];i!=-1;i=e[i].next){
            int y=e[i].v;
            if(dis1[y]>=dis+e[i].w){
                dis2[y]=dis1[y];
                dis1[y]=dis+e[i].w;
                q.push((node){dis1[y],y});
            }
            else if(dis2[y]>dis+e[i].w){
                dis2[y]=dis+e[i].w;
                q.push((node){dis2[y],y});//必须有 
            }
        }
    }
}//“必须有”因为不只考虑最优的

int main(){
    memset(head,-1,sizeof(head));
    memset(dis1,0x3f,sizeof(dis1));
    memset(dis2,0x3f,sizeof(dis2));
    scanf("%d%d",&n,&r);
    for(int i=1;i<=r;i++){
        int a,b,c;
        scanf("%d%d%d",&a,&b,&c);
        add(a,b,c);
        add(b,a,c);
    }
    dijkstra();
    printf("%d\n",dis2[n]);
}

次短路LuoguP2865

原文：https://www.cnblogs.com/Y15BeTa/p/10976977.html