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  • SPFA判断负环+链式前向星

    #include<iostream>
    #include<algorithm>
    #include<cstring>
    #include<vector>
    #include<map>
    #include<cmath>
    #include<cstdio>
    #include<queue>
    typedef long long ll;
    const int mod = 1e9+7;
    const int maxn = 1000000;
    const int inf = 0x3f3f3f3f;
    using namespace std;
    /*SPFA判断是否存在负环*/
    struct node
    {
        int u,v,w,next;
    }e[10050];
    
    int dis[10050],head[10050],cnt;
    bool vis[10050];
    int num[10050];//记录入队次数 
    int n,m,w; 
    void add(int u,int v,int w)
    {
        e[cnt].u = u;
        e[cnt].v = v;
        e[cnt].w = w;
        e[cnt].next = head[u];
        head[u] = cnt++;
    }
    bool spfa()
    {
        
        memset(vis,0,sizeof(vis));
        memset(num,0,sizeof(num));
        memset(dis,inf,sizeof(dis));
        queue<int> q;
        dis[1]=0;
        q.push(1);
        num[1]++;
        while(!q.empty())
        {
            int x = q.front();
            q.pop();
            vis[x]=0;
            for(int i = head[x];~i;i=e[i].next)
            {
                int v = e[i].v;
                if(dis[v] > dis[x]+e[i].w)
                {
                    dis[v] = dis[x] + e[i].w;
                    
                    if(!vis[v])
                    {
                        vis[v]=1;
                        
                        num[v]++;
                        
                        q.push(v); 
                        
                        if( num[v]>=n )
                        {
                            return true;
                        }
                    } 
                }
            }
        }
        return false;
    }
    int main()
    {
         ios::sync_with_stdio(false);
        cin.tie(0);cout.tie(0);
        int t;
        cin>>t;
        while(t--)
        {
            cnt = 0;
            memset(head,-1,sizeof(head));
            scanf("%d %d %d",&n,&m,&w);
            for(int i=0;i<m;i++)
            {
                int u,v,s;
                cin>>u>>v>>s;
                add(u,v,s);
                add(v,u,s);
            }
            for(int i=0;i<w;i++)
            {
                int u,v,s;
                cin>>u>>v>>s;
                add(u,v,-s);
            }
            if(spfa())
            {
                cout<<"YES"<<endl;
            }
            else
            {
                cout<<"NO"<<endl;
            }
        }
    }

     

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  • 原文地址:https://www.cnblogs.com/lightWh1te/p/13584386.html
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