最短路

 1 #include<iostream>
 2 #include<cstdio>
 3 #include<cmath>
 4 #include<algorithm>
 5 #include<queue>
 6 using namespace std;
 7 const int maxn=100000+10,INF=-1u>>1;
 8 struct Tedge{int x,y,w,next;}adj[maxn*2];int fch[maxn],ms=0;
 9 void AddEdge(int u,int v,int w){
10     adj[++ms]=(Tedge){u,v,w,fch[u]};fch[u]=ms;return;
11 }
12 bool vis[maxn];int dist[maxn],n,m;
13 void SPFA(){
14     queue<int>Q;memset(vis,false,sizeof(vis));
15     for(int i=1;i<=n+1;i++)dist[i]=INF;dist[1]=0;
16     Q.push(1);vis[1]=true;
17     while(!Q.empty()){
18         int u=Q.front();Q.pop();vis[u]=false;
19         for(int i=fch[u];i;i=adj[i].next){
20             int v=adj[i].y;
21             if(dist[v]>dist[u]+adj[i].w){
22                 dist[v]=dist[u]+adj[i].w;
23                 if(!vis[v]) vis[v]=true,Q.push(v);
24             }
25         }
26     } return ;
27 }
28 inline int read(){
29     int x=0,sig=1;char ch=getchar();
30     while(!isdigit(ch)){if(ch==‘-‘) sig=-1;ch=getchar();}
31     while(isdigit(ch)) x=10*x+ch-‘0‘,ch=getchar();
32     return x*=sig;
33 }
34 inline void write(int x){
35     if(x==0){putchar(‘0‘);return;}if(x<0) putchar(‘-‘),x=-x;
36     int len=0,buf[15];while(x) buf[len++]=x%10,x/=10;
37     for(int i=len-1;i>=0;i--) putchar(buf[i]+‘0‘);return;
38 }
39 void init(){
40     n=read();m=read();int a,b,c;
41     for(int i=1;i<=m;i++){
42         a=read();b=read();c=read();
43         AddEdge(a,b,c);//printf("-AddEdge-%d %d %d\n",k,j,c);
44     } return;
45 }
46 void work(){
47     SPFA();
48     //for(int i=1;i<=ms;i++)printf("-Edge- %d to %d is %d\n",adj[i].x,adj[i].y,adj[i].w);
49     //for(int i=1;i<=n+1;i++) printf("dist[%d]=%d\n",i,dist[i]);
50     return;
51 }
52 void print(){
53     if(dist[n+1]>=INF) puts("No Answer.");
54     else write(dist[n+1]),putchar(‘\n‘);
55     return;
56 }
57 int main(){
58     init();work();print();return 0;
59 }