CCF 201512-4 送货 (并查集+DFS，欧拉路)

#pragma comment(linker, "/STACK:1024000000,1024000000")
#include <cstdio>
#include <string>
#include <cstdlib>
#include <cmath>
#include <iostream>
#include <cstring>
#include <set>
#include <queue>
#include <algorithm>
#include <vector>
#include <map>
#include <cctype>
#include <cmath>
#include <stack>
#define freopenr freopen("in.txt", "r", stdin)
#define freopenw freopen("out.txt", "w", stdout)
using namespace std;

typedef long long LL;
typedef pair<int, int> P;
const int INF = 0x3f3f3f3f;
const double inf = 0x3f3f3f3f3f3f;
const LL LNF = 0x3f3f3f3f3f3f;
const double PI = acos(-1.0);
const double eps = 1e-8;
const int maxn = 1e4 + 5;
const int mod = 1e9 + 7;
const int dr[] = {-1, 0, 1, 0};
const int dc[] = {0, 1, 0, -1};
const char *Hex[] = {"0000", "0001", "0010", "0011", "0100", "0101", "0110", "0111", "1000", "1001", "1010", "1011", "1100", "1101", "1110", "1111"};
int n, m;
const int mon[] = {0, 31, 28, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
const int monn[] = {0, 31, 29, 31, 30, 31, 30, 31, 31, 30, 31, 30, 31};
inline int Min(int a, int b){ return a < b ? a : b; }
inline int Max(int a, int b){ return a > b ? a : b; }
inline LL Min(LL a, LL b){ return a < b ? a : b; }
inline LL Max(LL a, LL b){ return a > b ? a : b; }
inline bool is_in(int r, int c){
    return r >= 0 && r < n && c >= 0 && c < m;
}
vector<int> G[maxn];
int p[maxn], in[maxn];
int Find(int x) {  return x == p[x] ? x : p[x] = Find(p[x]); }
stack<int> ans;
bool vis[maxn][maxn];

void dfs(int u){
    for(int i = 0; i < G[u].size(); ++i){
        int v = G[u][i];
        if(!vis[u][v]){
            vis[u][v] = vis[v][u] = 1;
            dfs(v);
            ans.push(v);
        }
    }
}

bool judge(){
    int x = Find(1);
    int cnt = 0;
    for(int i = 1; i <= n; ++i){
        if(x != Find(i)) return false;
        if(in[i] & 1)  ++cnt;
        if(cnt > 2)  return false;
        sort(G[i].begin(), G[i].end());
    }

    if(cnt == 2 && in[1] % 2 == 0)  return false;
    return true;
}

void print(){
    printf("1");
    while(!ans.empty()){
        printf(" %d", ans.top());
        ans.pop();
    }
    printf("\n");
}

int main(){
    while(scanf("%d %d", &n, &m) == 2){
        for(int i = 1; i <= n; ++i)  G[i].clear(), p[i] = i;
        memset(in, 0, sizeof in);
        memset(vis, false, sizeof vis);
        int u, v;
        for(int i = 0; i < m; ++i){
            scanf("%d %d", &u, &v);
            G[u].push_back(v);
            G[v].push_back(u);
            int x = Find(u);
            int y = Find(v);
            if(x != y)  p[y] = x;
            ++in[u];  ++in[v];
        }

        if(!judge()){  printf("-1\n");  continue;  }
        dfs(1);
        print();
    }
    return 0;
}