Build a Palindrome

#include <bits/stdc++.h>
using namespace std;

 string maxi(string s1, string s2){
     int flag=0;
     if(s1==s2)
        return s1;
     if(s1.length()>s2.length())
     return s1;
     else if(s2.length()>s1.length())
     return s2;
     else{
         for(int i=0;i<s1.length();i++){
             if(s1[i]<s2[i]){
                 flag=1;
                 break;
             }
             if(s2[i]<s1[i]){
                 break;
             }
         }
         if(flag==1)
         return s1;
         else
         return s2;
     }
 }

 string palin(string s){
    int i=0, j=s.length()-1;
    string ans;
    while(i<=j){
        if(s[i]==s[j]){
            int shuru=i, khatam=j;
            int flag=0;
            string ans1, ans2;
            while(shuru<khatam){
                if(s[shuru]!=s[khatam]){
                    flag=1;
                    break;
                }
                ans1=ans1+s[shuru];
                ans2=s[khatam]+ans2;
                shuru++;
                khatam--;
            }
            if(shuru==khatam)
                ans1+=s[shuru];
            if(flag==0){
                ans=ans1+ans2;
                break;
            }
        }
        j--;
    }
    return ans;
}


string buildPalindrome(string a, string b) {
    string s;
    reverse(b.begin(), b.end());
    int m=a.length(), n=b.length();
    vector<vector<string> > dp;
    dp.reserve(10000);
    for(int i=0;i<=m;i++){
        vector<string> tempo;
        tempo.reserve(10000);
        for(int j=0;j<=n;j++){
            tempo.push_back("");
        }
        dp.push_back(tempo);
    }
    for(int i=1;i<=m;i++){
        for(int j=1;j<=n;j++){
            if(a[i-1]==b[j-1])
            dp[i][j]=dp[i-1][j-1]+a[i-1];
            else
            dp[i][j]="";
        }
    }
    for(int i=0;i<=m;i++){
        for(int j=0;j<=n;j++){
            if(dp[i][j].length()!=0){
                string temp=dp[i][j];
                reverse(temp.begin(), temp.end());
 s = maxi(s, dp[i][j] + maxi(palin(a.substr(i)), palin(b.substr(j))) + temp);
            }
        }
    }
    if(s=="")
    return "-1";
    return s;
}

int main()
{
    ofstream fout(getenv("OUTPUT_PATH"));

    int t;
    cin >> t;
    cin.ignore(numeric_limits<streamsize>::max(), '\n');

    for (int t_itr = 0; t_itr < t; t_itr++) {
        string a;
        getline(cin, a);

        string b;
        getline(cin, b);

        string result = buildPalindrome(a, b);

        fout << result << "\n";
    }

    fout.close();

    return 0;
}