图论--最长路--基于SPFA的调整模板

#include<iostream>
#include<queue>
#include<algorithm>
#include<set>
#include<cmath>
#include<vector>
#include<map>
#include<stack>
#include<bitset>
#include<cstdio>
#include<cstring>
#define Swap(a,b) a^=b^=a^=b
#define cini(n) scanf("%d",&n)
#define cinl(n) scanf("%lld",&n)
#define cinc(n) scanf("%c",&n)
#define cins(s) scanf("%s",s)
#define coui(n) printf("%d",n)
#define couc(n) printf("%c",n)
#define coul(n) printf("%lld",n)
#define speed ios_base::sync_with_stdio(0)
#define Max(a,b) a>b?a:b
#define Min(a,b) a<b?a:b
#define mem(n,x) memset(n,x,sizeof(n))
#define INF  0x3f3f3f3f
#define maxn  100010
#define Ege 100000000
#define Vertex 1005
#define esp  1e-9
#define mp(a,b) make_pair(a,b)
using namespace std;
typedef long long ll;
typedef pair<int,int> PII;
struct Node
{
    int to, lat, val; //边的右端点，边下一条边，边权
};
Node edge[1000005];
int head[1005],tot,dis[1005],N,M,vis[1005];
void add(int from, int to, int dis)
{
    edge[++tot].lat = head[from];
    edge[tot].to = to;
    edge[tot].val = dis;
    head[from] = tot;

}
void spfa(int s)
{

    for(int i=0;i<=N;i++) dis[i]=-INF;
    dis[0]=0;
    memset(vis, 0, sizeof(vis));
    vis[s] = 1;
    dis[s] = 0;
    queue<int>Q;
    Q.push(s);
    while (!Q.empty())
    {
        int u = Q.front();
        Q.pop();
        vis[u] = 0;
        for (int i = head[u]; i; i = edge[i].lat)
        {
            int to = edge[i].to;
            int di = edge[i].val;
            if (dis[to]<dis[u] + di)
            {
                dis[to] = dis[u] + di;
                if (!vis[to])
                {
                    vis[to] = 1;
                    Q.push(to);
                }
            }
        }
    }

}
int main()
{
    int t, x;

    memset(head, 0, sizeof(head));
    cini(N),cini(M);
    while (M--)
    {
        int a, b, dis;
        scanf("%d %d %d", &a, &b, &dis);
        add(a, b, dis);
    }
    spfa(1);
    if(dis[N]==-INF) {return cout<<-1<<endl,0;}
    cout<<dis[N]<<endl;

    return 0;
}