这真的没有什么好讲的，直接看代码吧。

#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#include <cmath>
using namespace std;

const int N = 1e4 + 10, M = 5e4 + 10;

int n, m, siz, path[M << 1];
int tot, Head[N], Edge[M << 1], Next[M << 1]; 

void add(int x, int y) {
    tot++;
    Edge[tot] = y;
    Next[tot] = Head[x];
    Head[x] = tot;
}

void dfs(int x) {
    for (int i = Head[x]; i; i = Head[x]) {
        int y = Edge[i]; Head[x] = Next[i];
        dfs(y);
    }
    path[++siz] = x;
}

int main() {
    cin >> n >> m;
    for (int i = 1; i <= m; i++) {
        int x, y; scanf("%d%d", &x, &y);
        add(x, y), add(y, x);
    }
    dfs(1);
    for (int i = siz; i >= 1; i--) printf("%d\n", path[i]);
    return 0;
}