ARC125C WA

// Problem: C - LIS to Original Sequence
// Contest: AtCoder - AtCoder Regular Contest 125
// URL: https://atcoder.jp/contests/arc125/tasks/arc125_c
// Memory Limit: 1024 MB
// Time Limit: 2000 ms
//
// Powered by CP Editor (https://cpeditor.org)

#include <assert.h>
#include <bits/stdc++.h>
using namespace std;
#define dbg(...) logger(#__VA_ARGS__, __VA_ARGS__)
template <typename... Args> void logger(string vars, Args &&... values)
{
    cerr << vars << " = ";
    string delim = "";
    (..., (cerr << delim << values, delim = ", "));
    cerr << endl;
}

template <class T> inline auto vv(int m) { return vector<vector<T>>(m, vector<T>(m)); }
template <class T> inline auto vv(int m, int n) { return vector<vector<T>>(m, vector<T>(n)); }
template <class T, T init> inline auto vv(int m) { return vector<vector<T>>(m, vector<T>(m, init)); }
template <class T, T init> inline auto vv(int m, int n) { return vector<vector<T>>(m, vector<T>(n, init)); }

template <class T> using mpq = priority_queue<T, vector<T>, greater<T>>;

using ll = long long;
using pii = pair<int, int>;
using vl = vector<ll>;
using vi = vector<int>;

int main(int argc, char **argv)
{
    int n, k;
    cin >> n >> k;
    vi a(k);
    vi b;
    set<int> s1;
    for (auto &x : a)
        cin >> x, s1.insert(x);
    for (int i = n; i >= 1; --i)
        if (s1.count(i) == 0)
            b.push_back(i);
    int blen = b.size();
    set<int> s;
    for (int i = 0; i + 1 < k; ++i) {
        cout << a[i] << ' ';
        s.insert(a[i]);
        while (b.empty() == false && b.back() < a[i] && blen - b.size() <= i) {
            // while (b.empty() == false && b.back() < a[i]) {
            int val = b.back();
            b.pop_back();
            s.insert(val);
            cout << val << ' ';
        }
    }
    for (int i = n; i > 0; --i) {
        if (s.count(i) == 0) {
            s.insert(i);
            cout << i << ' ';
        }
    }
    cout << endl;
    return 0;
};