Language: C++

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

#define pb(x) push_back(x)
#define memset0(x) memset((x), 0, sizeof(x))
#define memsetM1(x) memset((x), -1, sizeof(x))
#define F first
#define S second
typedef long long ll;
typedef unsigned long long ull;
typedef pair<int,int> pii;
typedef tuple<int, int, int> Tiii;
#define UNIQUE(v) (v).erase(unique((v).begin(), (v).end()), (v).end());
#define all(x) (x).begin(), (x).end()
#define chkbnd(i,j) 0<=i && i<n && 0<=j && j<m
#define precise(a) fixed<<setprecision(a)
#define isvowel(c) c=='a' || c=='e' || c=='i' || c=='o' || c=='u'

#define SQ(x) ((x)*(x))
#define issq(x) (((ll)(sqrt((x))))*((ll)(sqrt((x))))==(x))
#define mem(a,x) memset(a,x,sizeof(a))
#define inf 1e18
#define lg(r,n) (int)(log2(n)/log2(r))
#define fast ios_base::sync_with_stdio(false)
#define one(x) __builtin_popcount(x)

//#define iceil(n, x) (((n) + (x) - 1) / (x))
//return the minimum number >=n , which is divisible by x
//int next_popcount(int n){int c = (n & -n);int r = n+c;int p = r^n;int x = (p>>2)/c;return x  r;}
// Let, n e k ti onBit ache, this func return a serial combination of k onBit.

//struct BIT{
//    vector<ll> Tree;ll Size=0;void init(int n){Tree.assign(n+1,0);Size=n;}
//    void update(int indx,ll val){while(indx<=n){Tree[indx] += val;indx += (indx)&(-indx);}}
//    ll query(int indx){ll sum=0;while(indx>0)
//        {sum += Tree[indx];sum %= mod;indx -= (indx)&(-indx);}return sum;}
//    ll query(int l, int r){return (query(r) - query(l-1)+mod)%mod;}
//};
//ll bigmod(ll a, ll b){if(b==0) return 1%mod;ll x = bigmod(a,b/2);
//    x = (x*x)%mod;if(b%2==1) x = (x*a)%mod;return x;}
//ll egcd(ll a, ll b, ll &x, ll &y){if(a==0){x=0;y=1;return b;}
//    ll x1,y1;ll d =egcd(b%a, a,x1,y1);x = y1-(b/a)*x1;y=x1;return d;}


//have to check;
#define lcase(a) (char)tolower(a)
#define ucase(a) (char)toupper(a)
#define section(a,b,w) set_intersection(a.begin(), a.end(),b.begin(), b.end(),back_inserter(w));
#define union(a,b,w) set_union(a.begin(), a.end(),b.begin(), b.end(),back_inserter(w));
#define copy(a,w) copy(a.begin(), a.end(),back_inserter(w));
//

constexpr double PI = (double)acos(-1);
constexpr double EPS = (double)1e-10;
constexpr int dx[] = {0,1,0,-1};
constexpr int dy[] = {1,0,-1,0};
constexpr int dxx[] = {-1, 0, 0, 1, 0, -1, -1, 1, 1};
constexpr int dyy[] = {0, -1, 1, 0, 0, 1, -1, 1, -1};
inline int toInt(string s) { int v; istringstream sin(s); sin >> v; return v; }

#define bit(n) (1LL << (n))
#define bitset(a, b) (a) |= (1 << (b))
#define bitunset(a, b) (a) &= ~(1 << (b))
#define bitcheck(a, b) ((((a) >> (b)) & 1) == 1)
#define bitcount(a) __builtin_popcountll((a))
inline void bin(ll n){if (n > 1)bin(n>>1); cout<<(n&1);}
inline int binlen(ll x) { if(x==0) return 1; return floor(log2(double(x)))+1;}
#define FRO freopen("in.txt","r",stdin);
#define oFRO freopen("out.txt","w",stdout);
#define DEBUG(args...) do {cerr<<#args<<' '; print(args);} while(0);cerr<<endl;
template<typename T> void print(const T& v){cerr<<v<<' ';}
template<typename T1,typename... T2>
void print(const T1& first,const T2&... rest){print(first);print(rest...);}
template<class T>constexpr const T&_min(const T&x,const T&y){return x<y?x:y;}template<class T>constexpr const T&_max(const T&x,const T&y){return x<y?y:x;}
template<class T,class...Ts>constexpr const T&_min(const T&x,const Ts&...xs){return _min(x,_min(xs...));}
template<class T,class...Ts>constexpr const T&_max(const T&x,const Ts&...xs){return _max(x,_max(xs...));}
template<class T,class...Ts>void MIN(T&x,const Ts&...xs){x=_min(x,xs...);}template<class T,class...Ts>void MAX(T&x,const Ts&...xs){x=_max(x,xs...);}
#define min(...) _min(__VA_ARGS__)
#define max(...) _max(__VA_ARGS__)

ll gcd(ll a,ll b) {return b?gcd(b,a%b):a;}
// ==============================================================================================

ll dp[3003][3003];
string ss,tt;


class solution{
public:
        ll n,m,w,k,slen,tlen;
        string str="";

        go(ll i, ll j)
        {
                if(i<0|| j<0 ) return INT_MIN;
                if(dp[i][j]!=-1) return dp[i][j];
                return dp[i][j]=max(go(i,j-1),go(i-1,j),go(i-1,j-1)+(ss[i]==tt[j]));
        }

        void solve()
        {
                cin>>ss>>tt;
                slen=ss.size();
                tlen=tt.size();
                ss='*'+ss;
                tt='#'+tt;
                for(ll i=1;i<1003;i++)
                        for(ll j=1;j<1003;j++)
                                dp[i][j]=-1;
                dp[0][0]=0;
                go(slen,tlen);
                while(slen>=0 && tlen>=0 && dp[slen][tlen]>0)
                {
                      if(dp[slen][tlen]==dp[slen][tlen-1] )
                      {
                              tlen--;
                      }
                      else if( dp[slen][tlen]==dp[slen-1][tlen] )
                      {
                              slen--;
                      }
                      else
                      {
                              str+=ss[slen];
                              slen--;
                              tlen--;
                      }

                        //DEBUG(slen, tlen)
                }
                reverse(str.begin(),str.end());
                cout<<str;
        }
        ///---->make all int ll must<----
};

int main()
{
        ios::sync_with_stdio(0);
        cin.tie(0);
        solution ob;
        ob.solve();
	return 0;
}



















Compiler output:
a.cc:93:9: error: ISO C++ forbids declaration of 'go' with no type [-fpermissive]
   93 |         go(ll i, ll j)
      |         ^~