萌新看了一下午OI-Wiki没看懂，就去b站一个视频看到的，但一直输出1 2 5死循环

code：

#include <cstdio>
#include <iostream>
#define int long long
#define INF 9223372036854775800LL
using namespace std;
const int maxn = 1e5 + 10;

struct edge {
    int to, w, nxt;
    edge() { nxt = -1; }
} Graph[maxn];
int tot, head[maxn];
void addEdge(int u, int to, int w) {
    Graph[tot].to = to;
    Graph[tot].w = w;
    Graph[tot].nxt = head[u];
    head[u] = tot++;
}
signed main() {
    int n, m, flg; //有向/无向
    cin >> n >> m >> flg;
    for (int i = 1; i <= m; i++) {
        int x, y, v;
        cin >> x >> y >> v;
        if (flg) {
            addEdge(x, y, v);
        } else {
            addEdge(x, y, v);
            addEdge(y, x, v);
        }
    }
    cout << "input ok";
    for (int u = 1; u <= n; u++)
        for (int i = head[u]; ~i; i = Graph[i].nxt) {
            int v = Graph[i].to;
            int w = Graph[i].w;
            cout << u << " " << v << " " << w << endl;
        }
    return 0;
}

一直输出1 2 5

还有就是这题说的先按第一个数升序排列，再以链式前向星中的顺序输出即可。要怎么搞啊/kel