OJ-Problems-Source/SCU/4444_woshinannan741.cpp

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#include<cstdio>
#include<cstring>
#include<queue>
#include<set>
#include<algorithm>
using namespace std;
const int MAXN = 5e5+5;
const int INF = 0x3f3f3f3f;
typedef long long LL;
int head[MAXN],e;
LL dis[MAXN];
bool vis[MAXN];
struct Edge{
int v,nxt,w;
}E[MAXN<<1];
void init()
{
e=0;
memset(head,-1,sizeof head);
memset(vis,false,sizeof vis);
}
void add(int u,int v,int w)
{
E[e].v = v;
E[e].w = w;
E[e].nxt = head[u];
head[u] = e++;
}
struct QNode{
int v,c;
QNode(int _v,int _c){
v = _v;c=_c;
}
bool operator < (const QNode &a) const{
return c>a.c;
}
};
LL dijkstra(int n)
{
memset(dis,INF,sizeof dis);
priority_queue<QNode>Q;
dis[1] = 0;
Q.push(QNode(1,0));
while(!Q.empty())
{
QNode tmp = Q.top();Q.pop();
int u = tmp.v;
if(vis[u]) continue;
vis[u] = true;
for(int i=head[u];~i;i=E[i].nxt){
int v = E[i].v;
int w = E[i].w;
if(vis[v]) continue;
if(dis[u]+w<dis[v]){
dis[v] = dis[u]+w;
Q.push(QNode(v,dis[v]));
}
}
}
return dis[n];
}
LL BFS(int n,LL val)
{
set<int>ta,tb;
queue<int>Q;Q.push(1);
dis[1] = 0,dis[n] = INF;
for(int i=2;i<=n;i++) ta.insert(i);
while(!Q.empty())
{
int u = Q.front();Q.pop();
for(int i=head[u];~i;i=E[i].nxt){
int v = E[i].v;
if(!ta.count(v)) continue;
ta.erase(v);tb.insert(v);
}
for(set<int>::iterator it=ta.begin();it!=ta.end();it++){
Q.push(*it);
dis[*it] = dis[u] + val;
}
ta.swap(tb);tb.clear();
}
return dis[n];
}
int main()
{
int N,M;
LL A,B;
int u,v;
while(~scanf("%d%d%lld%lld",&N,&M,&A,&B))
{
init();
bool flag = false;
for(int i=0;i<M;i++){
scanf("%d%d",&u,&v);
add(u,v,A);add(v,u,A);
if(min(u,v)==1&&max(u,v)==N)flag =true;
}
if(!flag) printf("%lld\n",min(dijkstra(N),(LL)B));
else printf("%lld\n",min(BFS(N,B),(LL)A));
}
return 0;
}