求助92pts #17 #22WA

#include<bits/stdc++.h>
#define int long long
using namespace std;
#define getchar() (read.getc())
#define putchar(c) (print.putc(c))
#define puts(s) MYPUTS(s)
struct in {
    char buf[1 << 20], * p1, * p2;
    inline char getc() { return (p1 == p2 && (p2 = (p1 = buf) + fread(buf, 1, 1 << 20, stdin), p1 == p2) ? EOF : *p1++); }
    int operator()() {
        int x = 0, f = 1; char ch = getc();
        while (!isdigit(ch) && ch != EOF) { if (ch == '-')f = -1; ch = getc(); }
        while (isdigit(ch)) { x = x * 10 + ch - 48; ch = getc(); }
        return x * f;
    }
}read;
struct out {
    char buf[1 << 20], * p, * end;
    out() { p = buf; end = buf + (1 << 20); }
    inline void putc(char c) { if (p == end)fwrite(buf, 1, 1 << 20, stdout), p = buf; *p++ = c; }
    void operator()(int a) {
        if (a < 0)putc('-'), a = -a;
        if (a >= 10)(*this)(a / 10);
        putc(a % 10 ^ 48);
    }
    ~out() { fwrite(buf, 1, p - buf, stdout); }
}print;
inline void MYPUTS(const char* str) { for (int i = 0; str[i]; i++)putchar(str[i]); putchar('\n'); }

int n = read(), m = read();
vector<int>e[500010];

int sta[500010], idx;
bool vis[500010], h[500010], ed;
void tarjan(int d) {
    sta[++idx] = d, vis[d] = 1;
    for (vector<int>::iterator it = e[d].begin(); it != e[d].end(); it++) {
        if (sta[idx - 1] != *it) {
            if (vis[*it] == 1) {
                while (idx && sta[idx] != *it)h[sta[idx--]] = 1;
                h[*it] = ed = 1;
            }
            else tarjan(*it);
        }
        if (ed)break;
    }
    idx--, vis[d] = 0;
}

int t;

void dfs(int d, int up, int front) {
    if (t ^ d)print(d), putchar(' ');
    if (!h[d])
        for (auto&& i : e[d]) {
            if (vis[i])continue;
            vis[i] = 1, dfs(i, 0, 0);
        }
    else {
        int Max = *e[d].rbegin(), st=front, sec=up;
        for (auto&& i : e[d]) {
            if (vis[i])continue;
            if (i == Max)break;
            if (h[i]) { st = d, sec = *(&i + 1); break; }
        }
        for (auto&& i : e[d]) {
            if (vis[i])continue;
            if (h[i] && i > up && up && i==Max)
                t = front, memset(h, 0, sizeof(h)), dfs(front, 0, 0);
            else vis[i] = 1, dfs(i, sec, st);
        }
    }
}

signed main() {
    for (int i = 1; i <= m; i++) {
        int a = read(), b = read();
        e[a].emplace_back(b);
        e[b].emplace_back(a);
    }
    for (int i = 1; i <= n; i++)
        sort(e[i].begin(), e[i].end());
    tarjan(1), idx = 0;
    vis[1] = 1, dfs(1, 0, 0);
    return~EOF;
}