2017 第十场多校训练 HDU 6181 Two Paths 次短路+Dijkstra

/*
裸的次短路
不断更新v->u的次短路，直到v->u的次短路只比最短路小
*/
#include <vector>
#include <iostream>
#include <stdio.h>
#include <queue>
using namespace std;
#define ll long long
#define INF 1e18
#define MAXM 100100
struct edge{int to;ll w;};
typedef pair<ll,int>P;
int n,r;
ll d[MAXM];
ll d1[MAXM];
vector<edge>G[MAXM];
bool vis[MAXM];
void solve(){
priority_queue<P, vector<P>,greater<P> >que;
fill(d+1,d+n+1,INF);
fill(d1+1,d1+n+1,INF);
d[1]=0;
que.push(P(0,1));
while(!que.empty()){
P p=que.top();
que.pop();
int v=p.second;
if(d1[v]<p.first)continue;
for(int i=0;i<G[v].size();i++){
edge &e=G[v][i];
ll d2=p.first+e.w;
if(d[e.to]>d2){
swap(d[e.to],d2);
que.push(P(d[e.to],e.to));
}
if(d1[e.to]>d2&&d[e.to]<d2){
d1[e.to]=d2;
que.push(P(d1[e.to],e.to));
}
}
}
printf("%I64d\n",d1
);
}
int main(){
int t;
scanf("%d",&t);
while(t--){
scanf("%d %d",&n,&r);
for(int i=1;i<=n;i++){
G[i].clear();
}
int u,v;
ll w;
while(r--){
scanf("%d %d %I64d",&u,&v,&w);
G[u].push_back(edge{v,w});
G[v].push_back(edge{u,w});
}
solve();
}
return 0;
}

一种复杂的做法

#include <bits/stdc++.h>
#define next _next
using namespace std;
typedef long long ll;
const ll inf=0x3f3f3f3f3f3f3f;
const int MAXN=200000+10;
struct Rec{
int num;
ll len;
bool operator < (const Rec &a) const {
return len>a.len;
}
};
int u[MAXN*2],v[MAXN*2];
ll dis[MAXN/2],secondis[MAXN/2],w[MAXN*2];
int first[MAXN/2],next[MAXN*2];
int n,r;

void dijkstra()
{
priority_queue<Rec>que;
for (int i=1;i<n;i++){
dis[i]=inf;
secondis[i]=inf;
}
dis[0]=0;
secondis[0]=inf;
Rec temp;
temp.len=0;
temp.num=0;
que.push(temp);
while (!que.empty())
{
Rec head=que.top();
que.pop();
if (head.len>secondis[head.num]) continue;
int k=first[head.num];
while (k!=-1)
{
ll d=head.len+w[k];
if (dis[v[k]]>d)
{
swap(dis[v[k]],d);
temp.len=dis[v[k]];temp.num=v[k];
que.push(temp);
}
if (dis[v[k]]<d && secondis[v[k]]>d)
{
secondis[v[k]]=d;
temp.len=secondis[v[k]];temp.num=v[k];
que.push(temp);
}
k=next[k];
}
}
}