模拟队列

#include<iostream>
#include<algorithm>
#include<cstring>

using namespace std;

const int N =2510,M=6200*2+10;
int n,m,S,T;
int h[N],e[M],ne[M],w[M],idx;
int dist[N],q[N];
bool st[N];

void add(int a,int b,int c)
{
    e[idx]=b,w[idx]=c,ne[idx]=h[a],h[a]=idx++;
}

void spfa()
{
    memset(dist,0x3f,sizeof dist);
    dist[S]=0;

    int hh=0,tt=1;
    q[0]=S;
    st[S]=true;

    while(hh!=tt)
    {
        int t=q[hh++];
        if(hh==N)  hh=0;   出队
        st[t]=false;

        for(int i=h[t];~i;i=ne[i])
        {
            int j=e[i];
            if(dist[j]>dist[t]+w[i])
            {
                dist[j]=dist[t]+w[i];
                if(!st[j])
                {
                    q[tt++]=j;
                   if(tt==N)  tt=0;
                   //防止队列出界，让队尾为0；
                    st[j]=true;
                }
            }
        }
    }
}

int main()
{
    cin>>n>>m>>S>>T;

    memset(h,-1,sizeof h);
    for(int i=0;i<m;i++)
    {
        int a,b,c;
        cin>>a>>b>>c;
        add(a,b,c),add(b,a,c);
    }
    spfa();

    cout<<dist[T]<<endl;
    return 0;
}

STL

stl中的queue是循环队列

#include<bits/stdc++.h>
using namespace std;
const int N = 2000010;
int n, m, start, en;
int h[N], e[N], ne[N], w[N], idx;
int dist[N];
bool st[N];
void add(int a, int b, int c)
{
    e[idx] = b, w[idx] = c, ne[idx] = h[a], h[a] = idx ++;
} 
int spfa()
{
    memset(dist, 0x3f, sizeof dist);
    dist[start] = 0;
    st[start] = true;
    queue<int> q;
    q.push(start);
    while(q.size())
    {
        int t = q.front();
        q.pop();
        st[t] = false;
        for(int i = h[t]; i != -1; i = ne[i])
        {
            int j = e[i];
            if(dist[j] > dist[t] + w[i])
            {
                dist[j] = dist[t] + w[i];
                if(!st[j])
                {
                    st[j] = true;
                    q.push(j);
                }
            }
        }
    }
    return dist[en];
}
int main()
{
    memset(h, -1, sizeof h);
    cin >> n >> m >> start >> en;
    for(int i = 0; i < m; i ++)
    {
        int a, b, c;
        cin >> a >> b >> c;
        add(a, b, c);
        add(b, a, c);
    }
    int t = spfa();
    cout << t << endl;
    return 0;
}