(简单) POJ 3169 Layout，差分约束+SPFA。

#include <stdio.h>
#include <string.h>
#include <iostream>
#include <algorithm>
#include <vector>
#include <queue>
#include <set>
#include <map>
#include <string>
#include <math.h>
#include <stdlib.h>
#include <time.h>
    
using namespace std;

const int MaxN=1010;
const int MaxM=30100;
const int INF=1000000009;

struct Edge
{
    int to,next,cost;
};

Edge E[MaxM];
int head[MaxN],Ecou;

bool vis[MaxN];
int couNode[MaxN];

void init(int N)
{
    Ecou=0;
    for(int i=1;i<=N;++i)
    {
        head[i]=-1;
        couNode[i]=0;
        vis[i]=0;
    }
}

void addEdge(int u,int v,int w)
{
    E[Ecou].to=v;
    E[Ecou].cost=w;
    E[Ecou].next=head[u];
    head[u]=Ecou++;
}

bool SPFA(int lowcost[],int N,int start)
{
    int t,v;
    queue <int> que;

    for(int i=1;i<=N;++i)
        lowcost[i]=INF;
    lowcost[start]=0;

    que.push(start);
    couNode[start]=1;
    vis[start]=1;

    while(!que.empty())
    {
        t=que.front();
        que.pop();

        vis[t]=0;

        for(int i=head[t];i!=-1;i=E[i].next)
        {
            v=E[i].to;
            
            if(lowcost[v]>lowcost[t]+E[i].cost)
            {
                lowcost[v]=lowcost[t]+E[i].cost;

                if(!vis[v])
                {
                    vis[v]=1;
                    couNode[v]+=1;
                    que.push(v);

                    if(couNode[v]>N)
                        return 0;
                }
            }
        }
    }

    return 1;
}

int ans[MaxN];

int main()
{
    //freopen("in.txt","r",stdin);
    //freopen("out.txt","w",stdout);
    
    int N,ML,MD;
    int a,b,c;

    scanf("%d %d %d",&N,&ML,&MD);

    init(N);

    for(int i=1;i<=ML;++i)
    {
        scanf("%d %d %d",&a,&b,&c);

        addEdge(a,b,c);
    }

    for(int i=1;i<=MD;++i)
    {
        scanf("%d %d %d",&a,&b,&c);

        addEdge(b,a,-c);
    }

    for(int i=1;i<=N-1;++i)
        addEdge(i+1,i,0);

    if(!SPFA(ans,N,1))
        printf("-1\n");
    else if(ans[N]!=INF)
        printf("%d\n",ans[N]);
    else
        printf("-2\n");

    return 0;
}