SPFA 最短路径打印方法

#include <iostream>

#include <cstdlib>

#include <cstdio>

#include <algorithm>

#include <vector>

#include <queue>

#include <cmath>

#include <cstring>

using namespace std;

#define INF 0xfffffff

#define maxn 40



struct Edge

{

    int e, w;

    Edge(int e=0,int w=0) : e(e), w(w) {}

};

int Path[maxn], n, dist[maxn];

bool vis[maxn];

vector<Edge> G[maxn];



void Spfa(int Star,int End)

{

    Edge P, Pn;

    dist[Star] = 0;

    queue<Edge> Q;

    Q.push(Edge(Star,0));



    while( !Q.empty() )

    {

        P = Q.front();

        Q.pop();

        vis[P.e] = true;



        int len = G[P.e].size();



        for(int i=0; i<len; i++)

        {

            Pn = G[P.e][i];



            if(dist[Pn.e] > dist[P.e] + Pn.w)

            {

                dist[Pn.e] = dist[P.e] + Pn.w;

                Path[Pn.e] = P.e;

                if( !vis[Pn.e] )

                {

                    Q.push(Pn);

                    vis[Pn.e] = true;

                }

            }

        }

    }

}



void PutPath(int Star,int End)

{

    if(Star == End)

    {

        printf("%d", Star);

        return ;

    }



    PutPath(Star, Path[End]);



    printf("---->%d", End);

}

void Init()

{

    for(int i=1; i<=n; i++)

    {

        G[i].clear();

        dist[i] = INF;

        vis[i] = false;

        Path[i] = i;

    }

}



int main()

{

    int m;

    cin >> n >> m;



    Init();



    for(int i=1; i<=m; i++)

    {

        int a, b, c;

        cin >> a >> b >> c;

        G[a].push_back(Edge(b,c));

    }



    Spfa(1, n);



    printf("%d\n", dist[n]);



    PutPath(1,n);







    return 0;

}

/*

4 3

1 2 1

2 3 1

3 4 1

*/