1.Dijkstra(适合于稠密图)

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define endl '\n'
const ll inf=0x3f3f3f3f;
inline void FAST_IO() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
}
const int N=2e4+5;
int dist[N],vis[N],gap[N][N];
int n,m;
inline ll down(ll a,ll b){
    return a<b?a:b;
}
void dijkstra(){
    for(int i=1;i<=n;i++){
        dist[i]=inf;
        vis[i]=0;
    }
    dist[1]=0;
    while(true){
        int minNum=inf,ans=-1;
        for(int i=1;i<=n;i++){
            if(!vis[i]&&minNum>dist[i]){
                minNum=dist[i];
                ans=i;
            }
        }
        if(ans==-1)break;
        vis[ans]=1;
        for(int i=1;i<=n;i++){
            if(!vis[i]&&dist[i]>dist[ans]+gap[ans][i]){
                dist[i]=dist[ans]+gap[ans][i];
            }
        }
    }
    cout<<dist[n]<<endl;
}
signed main() {
    FAST_IO();
    while(cin>>n>>m){
        for(int i=1;i<=n;i++){
            for(int j=1;j<=n;j++){
                gap[i][j]=(i==j?0:inf);
            }
        }
        for(int i=0;i<m;i++){
            int a,b,v;
            cin>>a>>b>>v;
            gap[a][b]=gap[b][a]=down(gap[a][b],v);
        }
        dijkstra();
    }
    return 0;
}

2.堆优化版本(适合解决稀疏图)

#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define endl '\n'
const ll inf=0x3f3f3f3f;
inline void FAST_IO() {
    ios::sync_with_stdio(false);
    cin.tie(0);
    cout.tie(0);
}
const int MAXN=2e6;
const int N=1e4+5;
struct Edge{
    int to,val,nxt;
}e[MAXN];
int head[N],dist[N],vis[N];
int n,m,tot;
inline void add(int from,int to,int val){
    e[tot]=Edge{to,val,head[from]};
    head[from]=tot++;
}
struct node{
    int index,dist;
    friend bool operator < (const node &a,const node &b){
        return a.dist>b.dist;
    }
};
void dijkstra(){
    for(int i=1;i<=n;i++){
        dist[i]=inf;
        vis[i]=0;
    }
    dist[1]=0;
    priority_queue<node>q;
    q.push(node{1,0});
    while(!q.empty()){
        node now=q.top();
        q.pop();
        if(vis[now.index]==1)continue;
        vis[now.index]=0;
        for(int i=head[now.index];i!=-1;i=e[i].nxt){
            int to=e[i].to;
            int val=e[i].val;
            if(dist[to]>dist[now.index]+val){
                dist[to]=dist[now.index]+val;
                q.push(node{to,dist[to]});
            }
        }
    }
    cout<<dist[n]<<endl;
}
signed main() {
    FAST_IO();
    while(cin>>n>>m){
        memset(head,-1,sizeof(head));
        tot=0;
        for(int i=0;i<m;i++){
            int a,b,v;
            cin>>a>>b>>v;
            add(a,b,v);
            add(b,a,v);
        }
        dijkstra();
    }
    return 0;
}