SPFA 超级源点 判断负环

AcWing 852. spfa判断负环

#include <bits/stdc++.h>
using namespace std;

const int N = 2005, M = 10005;

int head[N], cnt;
int n, m;
int dis[N], backup[N];
int step[N];  //到当前点最短路径跳转的步数
bool st[N];

struct
{
   
    int v, w;
    int nxt;
} edges[M];

int spfa()
{
   
    memset(dis, 0x3f, sizeof dis);
    memset(st, 0, sizeof st