此代码错误，但可以过（其他 oj 上过不了）。

#include <bits/stdc++.h>
using namespace std;
const int N = 26005;
int n, m, a, b, idx, tmp, top, col, hd[N], dfn[N], low[N], co[N], st[N];
struct node {
	int to, nxt;
}e[N << 1];
inline void add(int u, int v){
	e[++idx].nxt = hd[u], e[idx].to = v, hd[u] = idx;
}
inline int find(int x){
	if(x % 2) return x + 1;
	return x - 1; 
}
inline void tarjan(int u){
	dfn[u] = low[u] = ++tmp, st[++top] = u;
	for(int i = hd[u]; i; i = e[i].nxt){
		int v = e[i].to;
		if(!dfn[v]){
			tarjan(v);
			low[u] = min(low[u], low[v]);
        } else if (!co[v]) low[u] = min (low[u], dfn[v]);
	}
	if(dfn[u] == low[u]){
		co[u] = ++col;
		while(st[top] != u) co[st[top]] = col, top--;
		top--;
	}
}
signed main(){
    ios::sync_with_stdio(0);
    cin.tie(0), cout.tie(0);
    cin >> n >> m;
	for(int i = 1; i <= m; i++){
        cin >> a >> b;
		add(a, find(b)), add(b, find(a));
	}
    for(int i = 1; i <= n * 2; i++) if(!dfn[i]) tarjan(i);
    for(int i = 1; i <= n * 2; i += 2){
        if(co[i] == co[i + 1]){
            cout << "NIE\n";
            return 0;
        }
    }
    for(int i = 1; i <= n * 2; i += 2){
        if(co[i] < co[i + 1]) cout << i << "\n";
        else cout << i + 1 << "\n";
    }
	return 0;
}