最短路

Spfa：

#include<iostream>
#include<cstdio>
#include<cmath>
#include<algorithm>
#include<queue>
using namespace std;
const int maxn=100000+10,INF=-1u>>1;
struct Tedge{int x,y,w,next;}adj[maxn*2];int fch[maxn],ms=0;
void AddEdge(int u,int v,int w){
    adj[++ms]=(Tedge){u,v,w,fch[u]};fch[u]=ms;return;
}
bool vis[maxn];int dist[maxn],n,m;
void SPFA(){
    queue<int>Q;memset(vis,false,sizeof(vis));
    for(int i=1;i<=n+1;i++)dist[i]=INF;dist[1]=0;
    Q.push(1);vis[1]=true;
    while(!Q.empty()){
        int u=Q.front();Q.pop();vis[u]=false;
        for(int i=fch[u];i;i=adj[i].next){
            int v=adj[i].y;
            if(dist[v]>dist[u]+adj[i].w){
                dist[v]=dist[u]+adj[i].w;
                if(!vis[v]) vis[v]=true,Q.push(v);
            }
        }
    } return ;
}
inline int read(){
    int x=0,sig=1;char ch=getchar();
    while(!isdigit(ch)){if(ch=='-') sig=-1;ch=getchar();}
    while(isdigit(ch)) x=10*x+ch-'0',ch=getchar();
    return x*=sig;
}
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;
}
void init(){
    n=read();m=read();int a,b,c;
    for(int i=1;i<=m;i++){
        a=read();b=read();c=read();
        AddEdge(a,b,c);//printf("-AddEdge-%d %d %d
",k,j,c);
    } return;
}
void work(){
    SPFA();
    //for(int i=1;i<=ms;i++)printf("-Edge- %d to %d is %d
",adj[i].x,adj[i].y,adj[i].w);
    //for(int i=1;i<=n+1;i++) printf("dist[%d]=%d
",i,dist[i]);
    return;
}
void print(){
    if(dist[n+1]>=INF) puts("No Answer.");
    else write(dist[n+1]),putchar('
');
    return;
}
int main(){
    init();work();print();return 0;
}