spfa最短路径

C++代码

#include <iostream>
#include <deque>
#include <stack>
#include <vector>
using namespace std;

const int MAXN=100;
const int INF=0x7FFFFFFF;

struct edge
{
    int to,weight;
};

vector<edge> adjmap[MAXN];//邻接表
bool in_queue[MAXN];//顶点是否在队列中
int in_sum[MAXN];//顶点入队次数
int dist[MAXN];//源点到各点的最短路径
int path[MAXN];//存储到达i的前一个顶点
int nodesum;//顶点数
int edgesum;//边数

bool SPFA(int source)
{
    deque<int> dq;
    int i,j,x,to;
    for(i=1;i<=nodesum;i++)
    {
        in_sum[i]=0;
        in_queue[i]=false;
        dist[i]=INF;
        path[i]=-1;
    }
    dq.push_back(source);
    in_sum[source]++;
    dist[source]=0;
    in_queue[source]=true;
//初始化完成

    while(!dq.empty())
    {
        x=dq.front();
        dq.pop_front();
        in_queue[x]=false;
        for(i=0;i<adjmap[x].size();i++)
        {
            to=adjmap[x][i].to;
            if((dist[x]<INF)&&(dist[to]>dist[x]+adjmap[x][i].weight))
            {
                dist[to]=dist[x]+adjmap[x][i].weight;
                path[to]=x;
                if(!in_queue[to])
                {
                    in_queue[to]=true;
                    in_sum[to]++;
                    if(in_sum[to]==nodesum) return false;
                    if(!dq.empty())
                    {
                        if(dist[to]>dist[dq.front()]) dq.push_back(to);
                        else dq.push_front(to);
                    }else dq.push_back(to);
                }
            }
        }
    }
    return true;
}

void Print_Path(int x)
{
    stack<int> s;
    int w=x;
    while(path[w]!=-1)
    {
        s.push(w);
        w=path[w];
    }
    cout<<"顶点1到顶点"<<x<<"的最短路径长度为："<<dist[x]<<endl;
    cout<<"所经过的路径为：1";
    while(!s.empty())
    {
        cout<<s.top()<<"";
        s.pop();
    }
    cout<<endl;
}

int main()
{
    int i,s,e,w;
    edge temp;
    cout<<"输入顶点数和边数：";
    cin>>nodesum>>edgesum;
    for(i=1;i<=nodesum;i++)
    adjmap[i].clear();//清空邻接表
    for(i=1;i<=edgesum;i++)
    {
        cout<<"输入第"<<i<<"条边的起点、终点还有对应的权值：";
        cin>>s>>e>>w;
        temp.to=e;
        temp.weight=w;
        adjmap[s].push_back(temp);
    }
    if(SPFA(1))
    {
        for(i=2;i<=nodesum;i++) Print_Path(i);
    } else cout<<"图中存在负权回路"<<endl;
    return 0;
}