Codeforces 911E - Stack Sorting

#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define pb push_back
#define meme(a,b) memset(a,b,sizeof(a))

const int N=2e5+5;
bool vis[N];
int a[N];
stack<int>s;
int main(){
    ios::sync_with_stdio(false);
    cin.tie(0);
    int n,k;
    cin>>n>>k;
    int temp=1;
    for(int i=1;i<=k;i++){
        cin>>a[i];
        vis[a[i]]=true;
        s.push(a[i]);
        while(s.size()&&s.top()==temp){
            s.pop();
            temp++;
        }
    }
    while(s.size()&&s.top()>temp||n+1>temp){
        int t;
        if(s.size())t=s.top();
        else t=n+1;
        for(int i=t-1;i>=temp;i--){
            if(vis[i]){
                cout<<-1<<endl;
                return 0;
            }
            else s.push(i),a[++k]=i,vis[i]=true;
        }
        while(s.size()&&s.top()==temp){
            s.pop();
            temp++;
        }
    }
    if(s.size())cout<<-1<<endl;
    else for(int i=1;i<=n;i++)cout<<a[i]<<‘ ‘;
    cout<<endl;
    return 0;
}