题解

#include<bits/stdc++.h>
#define ll long long
#define inf 0x3f3f3f3f
#define pb push_back
#define rep(i,a,b) for(int i=a;i<b;i++)
#define rep1(i,b,a) for(int i=b;i>=a;i--)
using namespace std;
const int N=1e5+100;
ll arr[4][4];
int main()
{
    string str1;
    string str2;
    cin>>str1>>str2;
    queue<char>q1;
    queue<char>q2;
    stack<char>st;
    rep(i,0,str1.size())
        q1.push(str1[i]);
    rep(i,0,str2.size())
        q2.push(str2[i]);
    map<char,int>mp1;
    int pp=1;
    int cnt=0;
    while(cnt<1e3)
    {
        cnt++;
        if(pp&&q1.empty())
            break;
        if(!pp&&q2.empty())
            break;
        if(pp)
        {
            char a=q1.front();
            //cout<<1<<' '<<a<<endl;
            q1.pop();
            if(mp1[a])
            {
                //cout<<"1win"<<endl;
                q1.push(a);
                while(1)
                {
                    char s=st.top();
                    st.pop();
                    mp1[s]--;
                    q1.push(s);
                    if(s==a)
                        break;
 
                }
                pp=!pp;
            }
            else
                st.push(a),mp1[a]++;
            if(q1.empty())
                break;
        }
        else
        {
            char a=q2.front();
            //cout<<2<<' '<<a<<endl;
            q2.pop();
            if(mp1[a])
            {
                q2.push(a);
                //cout<<"2win"<<endl;
                while(1)
                {
                    char s=st.top();
                    st.pop();
                    mp1[s]--;
                    q2.push(s);
                    if(s==a)
                        break;
                }
                pp=!pp;
            }
            else
                st.push(a),mp1[a]++;
            if(q2.empty())
                break;
        }
        pp=!pp;
    }
    if(cnt==1e3)
    {cout<<-1<<endl;return 0;}
    if(q1.empty())
    {
        while(!q2.empty())
        {
            cout<<q2.front();
            q2.pop();
        }
    }
    else if(q2.empty())
    {
        while(!q1.empty())
        {
            cout<<q1.front();
            q1.pop();
        }
    }
    cout<<endl;
    return 0;
}