使用取模操作来实现线性表循环队列
插入后 tail %= N
删除后 head %= N
其中N是队列最大长度

#include<stdio.h>
#include<string.h>
#include<stdbool.h>

#define N 2010
#define M 10010
#define INF 0x3f3f3f3f

int n, m;
int dist[N];
int queue[N];
bool inQue[N];
int head, tail;
int h[N], cnt;
int count[N];

struct edge{
    int to;
    int next;
    int weight;
}E[M];

void add(int v, int w, int weight){
    E[++cnt].next = h[v];
    E[cnt].to = w;
    E[cnt].weight = weight;
    h[v] = cnt;
}

bool spfa(){

    for(int i = 1; i <= n; i++){  
        queue[tail++] = i;
        inQue[i] = true;
    }

    while(head != tail){
        int t = queue[head++];
        head %= N;
        inQue[t] = false;

        for(int i = h[t]; i != -1; i = E[i].next){
            int u = E[i].to;
            if(dist[t] + E[i].weight < dist[u]){
                dist[u] = dist[t] + E[i].weight;
                count[u] = count[t] + 1;

                if(count[u] >= n) return true;
                if(!inQue[u]){
                    queue[tail++] = u;
                    tail %= N;
                    inQue[u] = true;
                }
            }
        }
    }
    return false;
}


int main(){

    scanf("%d %d", &n, &m);

    memset(h, -1, sizeof h);
    for(int i = 1; i <= m; i++){
        int a, b, w;
        scanf("%d %d %d", &a, &b, &w);
        if(a == b) add(a, b, 0);
        else  add(a, b, w);
    }

    if(spfa())  printf("Yes");
    else  printf("No");

    return 0;
}