打印栈的出栈序列

#include<bits/stdc++.h> 
using namespace std;
vector<int> ppp;
int n;
//vector<int> temp;
void dfs(int index,stack<int> s,vector<int> v,int &num){
    for(int i=s.size();i>=0;i--){
        stack<int> stemp(s);
        vector<int> vtemp(v);
        for(int j=1;j<=i;j++){
            int top=stemp.top();
            stemp.pop();
            vtemp.push_back(top);
        }
        stemp.push(ppp[index]);
        if(index==n){
            num++;
            for(auto it=vtemp.begin();it!=vtemp.end();it++){
                cout<<*it;
            }
            while(stemp.empty()==false){
                cout<<stemp.top();
                stemp.pop();
            }
            cout<<endl;
        }else{
            dfs(index+1,stemp,vtemp,num);
        }
    }
}
int main()
{
    //freopen("a.in","r",stdin);
    while(scanf("%d",&n)!=EOF){
        ppp.clear();
        ppp.push_back(0);
        for(int i=1;i<=n;i++){
            ppp.push_back(i);
        }
        int num=0;
        stack<int> s;
        vector<int> v;
        dfs(1,s,v,num);
        cout<<num<<endl;
    }
    return 0;
}