本着练习的角度，使用dijkstra spfa floyd 算法完成本题，巩固一下模板…大佬勿喷....

spfa和dijikstra

只需要将main的sfpa换成dijkstra即可切换

#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue>
#define x first
#define y second

using namespace std;
typedef pair<int,int> PII;
const int N = 210 * 2;
int e[N],ne[N],w[N],h[N],dist[N],idx;
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 n,m;

int dijkstra()
{
    priority_queue<PII,vector<PII>,greater<PII>> heap;
    memset(dist,0x3f,sizeof dist);
    heap.push({0,1});
    dist[1]=0
    while(heap.size())
    {
        auto t = heap.top();
        heap.pop();
        int ver = t.y,distance = t.x;
        //cout << ver << endl;
        if(st[ver])  continue;
        st[ver] = true;

        for(int i = h[ver]; ~i; i = ne[i])
        {
            int j = e[i];
            if(dist[j] > distance + w[i])
            {
                dist[j] = distance + w[i];
                heap.push({dist[j],j});
            }
        }
    }
    int res = -0x3f3f3f3f;
    for(int i = 1; i <= n; i ++)
    {
        if(dist[i]==0x3f3f3f3f) return -1;
        res = max(res,dist[i]);

    }
    return res;

}

int spfa()
{
    queue<int> q;
    memset(dist,0x3f,sizeof dist);
    dist[1] = 0;
    q.push(1);

    while(q.size())
    {
        int t = q.front();
        q.pop();
        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])
                {
                    st[j] = true;
                    q.push(j);
                }
            }
        }
    }
    int res = -0x3f3f3f3f;
    for(int i = 1; i <= n; i ++)
    {
        if(dist[i] == 0x3f3f3f3f) return -1;
        res = max(res,dist[i]);

    }
    return res;


}


int main()
{

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


    return 0;
}

朴素版dijkstra

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

using namespace std;
const int N = 110;
int g[N][N];
int dist[N];
int n,m;
bool st[N];
int dijkstra()
{
    memset(dist,0x3f,sizeof dist);
    dist[1] = 0;

    for(int i = 1; i < n; i ++)
    {
        int t = 0;
        for(int j = 1; j <= n; j ++)    //找出未被标记中最小的点
        {
            if(!st[j] && (t == 0 || dist[t] > dist[j]))
                t = j;
        }
        st[t] = true;                   //标记已使用
        //cout << t << " "; //printf调试法
        for(int k = 1; k <= n; k ++)    //用最小的点，更新其他点
            dist[k] = min(dist[k],dist[t] + g[t][k]);
    }
    int res = -1;
    for(int i = 1; i <= n; i ++)
    {
        if(dist[i] == 0x3f3f3f3f) return -1;
        res = max(res,dist[i]);
    }
    return res;
}
int main()
{
    cin >> n >> m;
    memset(g,0x3f3f3f3f,sizeof g);
    for(int i = 1; i <= m; i ++)
    {
        int a,b,c;
        cin >> a >> b >> c;
        if(a == b) continue;
        g[a][b] = min(g[a][b],c);
        g[b][a] = min(g[b][a],c);
    }
    cout <<  dijkstra() << endl;

    return 0;
}

Floyd

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

using namespace std;

const int N = 110, INF = 0x3f3f3f3f;

int n, m;
int d[N][N];

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

    memset(d, 0x3f, sizeof d);
    for (int i = 0; i < m; i ++ )
    {
        int a, b, c;
        cin >> a >> b >> c;
        d[a][b] = d[b][a] = min(d[a][b], c);
    }

    for (int k = 1; k <= n; k ++ )
        for (int i = 1; i <= n; i ++ )
            for (int j = 1; j <= n; j ++ )
                d[i][j] = min(d[i][j], d[i][k] + d[k][j]);

    int res = 0;
    for (int i = 1; i <= n; i ++ )
        if (d[1][i] == INF)
        {
            res = -1;
            break;
        }
        else res = max(res, d[1][i]);

    cout << res << endl;

    return 0;
}