COJ 0579 4020求次短路的长度

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<queue>
#include<cstring>
#define PAU putchar(' ')
#define ENT putchar('\n')
using namespace std;
const int maxn=5000+10,maxm=200000+10,inf=1e8;
struct ted{int x,y,w;ted*nxt;}adj[maxn<<1],*fch[maxn],*ms=adj;
void add(int x,int y,int w){
*ms=(ted){x,y,w,fch[x]};fch[x]=ms++;*ms=(ted){y,x,w,fch[y]};fch[y]=ms++;return;
}
int n,m;queue<int>Q;
struct solver{
bool inq[maxn];int d[maxn];
void spfa(int S){
for(int i=1;i<=n;i++)d[i]=inf,inq[i]=false;d[S]=0;queue<int>Q;Q.push(S);
while(!Q.empty()){
int u=Q.front();Q.pop();inq[u]=false;
for(ted*e=fch[u];e;e=e->nxt){
int v=e->y;
if(d[v]>d[u]+e->w){
d[v]=d[u]+e->w;
if(!inq[v])Q.push(v),inq[v]=true;
}
}
}return;
}
}p1,p2;
inline int read(){
int x=0,sig=1;char ch=getchar();
for(;!isdigit(ch);ch=getchar())if(ch=='-')sig=0;
for(;isdigit(ch);ch=getchar())x=10*x+ch-'0';
return sig?x:-x;
}
inline void write(int x){
if(x==0){putchar('0');return;}if(x<0)putchar('-'),x=-x;
int len=0,buf[15];while(x)buf[len++]=x%10,x/=10;
for(int i=len-1;i>=0;i--)putchar(buf[i]+'0');return;
}
int ans=inf,midist;
void init(){
n=read();m=read();int x,y,w;
for(int i=1;i<=m;i++){
x=read();y=read();w=read();add(x,y,w);
}
p1.spfa(1);p2.spfa(n);midist=p1.d
;//write(midist);ENT;
return;
}
void work(){
int size=ms-adj-1;
for(int i=0;i<=size;i+=2){
int u=adj[i].x,v=adj[i].y,w=adj[i].w;
int d1=p1.d[u]+w+p2.d[v],d2=p2.d[u]+w+p1.d[v];
if(d1!=midist)ans=min(ans,d1);
if(d2!=midist)ans=min(ans,d2);
}
return;
}
void print(){
write(ans);
return;
}
int main(){init();work();print();return 0;}