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题意：确定图中有无负圈

1 spfa 邻接矩阵实现

#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <vector>
#include <queue>
using namespace std;
const int maxe = 7000 , maxv= 515 , INF =1e9 ;
struct Edge{int to , cost ;};
vector <Edge> G[maxe] ;
int dist[maxv] , n , used[maxv] , vis[maxv];

bool spfa(int s)
{
    fill(dist , dist + n +1 , INF) ;
    fill(vis , vis +n + 1 , 0 ) ;
    fill(used , used + n +1, 0 ) ;
    dist[s] = 0 ;
    queue<int> que ;
    que.push(s) ; vis[s] = 1 ; used[s] ++ ;
    while(!que.empty())
    {
        int x = que.front() ; que.pop() ; vis[x] = 0 ;
        for(int i = 0 ; i < G[x].size() ; i ++)
        {
            Edge e = G[x][i] ;
            if(dist[e.to] > dist[x] + e.cost)
            {
                dist[e.to] = dist[x] + e.cost ;
                if(!vis[e.to])
                {
                    vis[e.to] = 1 ;
                  if(++used[e.to] > n - 1) return false ;
                    que.push(e.to) ;
                }
            }
        }
    }
 return true ;
}


int main()
{
    //freopen("a.txt" , "r" , stdin ) ;
    int t , m , W , u ,v, w ;
    Edge edge ;
    scanf("%d" , &t) ;
    for(int ca = 1 ; ca <= t ; ca ++)
    {
        scanf("%d%d%d" , &n , &m, &W) ;
        for(int i = 1 ; i <= n ; i ++) G[i].clear() ;
        for(int i = 1 ; i <= m ; i ++)
        {
            scanf("%d%d%d" , &u , &v ,&w) ;
            edge.to = v , edge.cost = w ;
            G[u].push_back(edge) ;
            edge.to = u ;
            G[v].push_back(edge) ;
        }
        for(int i = 1 ; i <= W ; i ++)
        {
            scanf("%d%d%d" , &u, &v , &w) ;
             edge.to = v , edge.cost = -w ;
             G[u].push_back(edge) ;
        }
        if(!spfa(1)) printf("YES\n") ;
        else printf("NO\n") ;
    }
    return 0;
}

2 spfa 链式前向星

#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <vector>
#include <queue>
using namespace std;
const int maxe = 7000 , maxv= 515 , INF =1e9 ;
struct Edge{int to , cost , next;}edge[maxe];

int top , n , used[maxv] , vis[maxv] , head[maxv] , dist[maxv] ;

void add_edge(int u , int v , int w)
{
    edge[top].to = v ;
    edge[top].cost = w ;
    edge[top].next = head[u] ;
    head[u] = top ++ ;
}

bool spfa(int s)
{
    fill(dist , dist + n + 1 , INF) ;
    fill(vis , vis + n + 1 , 0 ) ;
    fill(used , used + n + 1 , 0) ;
    queue<int > que ;
    dist[s] = 0 ; used[s] ++ ; vis[s] = 1 ;
    que.push(s) ;
    while(!que.empty())
    {
        int u = que.front() ; que.pop() ; vis[u] = 0 ;
        for(int i = head[u] ; i!= -1 ; i = edge[i].next)
        {
            Edge e = edge[i] ;
            if(dist[e.to] > dist[u] + e.cost)
            {
                dist[e.to] = dist[u] + e.cost ;
                if(!vis[e.to])
                {
                    vis[e.to] = 1 ;
                    if(++used[e.to] > n - 1) return false ;
                    que.push(e.to) ;
                }
            }
        }
    }
    return true ;
}

int main()
{
    //freopen("a.txt" , "r" , stdin ) ;
    int t , m , w , u , v , cost ;
    scanf("%d" , &t) ;
    while(t--)
    {
        scanf("%d%d%d" , &n , &m , &w) ;
        for(int i = 1 ; i <= n ; i ++) head[i] = -1 ;
        top = 0 ;
        for(int i = 1 ; i <= m ; i ++)
        {
            scanf("%d%d%d" , &u , &v , &cost) ;
            add_edge(u , v , cost) ;
            add_edge(v , u , cost) ;
        }

        for(int i = 1 ; i <= w ; i ++)
        {
            scanf("%d%d%d" , &u , &v , &cost) ;
            add_edge(u , v , -cost) ;
        }

        if(!spfa(1)) printf("YES\n") ;
        else printf("NO\n") ;
    }
    return 0 ;
}

3 Bellmon-Ford

#include <iostream>
#include <stdio.h>
#include <algorithm>
#include <string.h>
#include <vector>
#include <queue>
using namespace std;
const int maxe = 7000 , maxv= 515 , INF =1e9 ;
struct Edge{int to , cost , from;}edge[maxe];

int dist[maxv] , n , top ;

void add_edge(int u , int v  , int w)
{
    edge[top].from = u ;
    edge[top].to = v ;
    edge[top++].cost = w ;
}

bool find_negative_loop()
{
    memset(dist , sizeof(dist) , 0) ;
    for(int i = 0 ; i < n ; i ++)
    {
        for(int j = 0 ; j < top ; j ++)
        {
            Edge es = edge[j] ;
            if(dist[es.to]  > dist[es.from] + es.cost)
            {
                dist[es.to] =  dist[es.from] + es.cost ;
                if(i == n - 1 ) return true ;
            }
        }
    }
    return false ;
}

int main()
{
    //freopen("a.txt" , "r" , stdin ) ;
    int t ,  m , w , from , to , cost ;
    scanf("%d" , &t) ;
    while(t --)
    {
        scanf("%d%d%d" , &n , &m , &w) ;
        top = 0 ;  // 注意初始化
        for(int i = 1 ; i <= m ; i ++ )
        {
            scanf("%d%d%d" , &from , &to , &cost) ;
            add_edge(from , to , cost) ;
            add_edge(to , from , cost ) ;
        }

        for(int i = 1 ; i <= w ; i ++ )
        {
            scanf("%d%d%d" , &from , &to , &cost) ;
            add_edge(from , to , -cost) ;
        }

        if(find_negative_loop()) printf("YES\n") ;
        else printf("NO\n") ;
    }
    return 0 ;
}