Language: C++

#include<bits/stdc++.h>
//using namespace std;
#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#define rep(i,j,n) for(ll i=(ll)(j);i<(ll)(n);i++)
#define REP(i,j,n) for(ll i=(ll)(j);i<=(ll)(n);i++)
#define per(i,j,n) for(ll i=(ll)(j);(ll)(n)<=i;i--)
#define ll long long
#define ALL(a) (a).begin(),(a).end()
#define disup(A,key) distance(A.begin(),upper_bound(ALL(A),(ll)(key)))
#define dislow(A,key) distance(A.begin(),lower_bound(ALL(A),(ll)(key)))
#define pb emplace_back
#define mp std::make_pair
//
#define endl "\n"
//using std::endl;
using std::cin;
using std::cout;
using std::vector;
using std::string;
using std::upper_bound;
using std::lower_bound;
using vi=vector<ll>;
using vii=vector<vi>;
using pii=std::pair<ll,ll>;
//
constexpr ll MOD=1e9+7;
//constexpr ll MOD=998244353;
//constexpr ll MOD=10000000;
//constexpr ll MOD=1e5;
constexpr ll MAX=3e6;
constexpr ll INF=(1ll<<60);
template<class T>
class prique :public std::priority_queue<T, std::vector<T>, std::greater<T>> {};
template<typename T>
struct Segment_tree{
    ll N;
    T mem;
    vector<T> node;
    Segment_tree(vector<T> &X,T m):mem(m){
        ll sz=X.size();
        N=1;
        while(N<sz) N*=2;
        node.resize(2*N-1,mem);
        rep(i,0,sz) node[N-1+i]=X[i];
        per(i,N-2,0){
            node[i]=Compare(node[i*2+1],node[i*2+2]);
        }
    }
    T Compare(T &A,T &B){
        return std::max(A,B);
    }
    void update(ll X,T val){
        X+=N-1;
        node[X]=val;
        while(X>0){
            X=(X-1)/2;
            node[X]=Compare(node[X*2+1],node[X*2+2]);
        }
    }
    T Query(ll a,ll b,ll now,ll l,ll r){ //[a,b),[l,r)
        if(r<0) r=N;
        if(r<=a||b<=l) return mem;
        if(a<=l&&r<=b) return node[now];
        auto vl=Query(a,b,now*2+1,l,(l+r)/2),vr=Query(a,b,now*2+2,(l+r)/2,r);
        return Compare(vl,vr);
    }
};
struct Binary_indexed_tree{
    int N;
    vi bit;
    Binary_indexed_tree(int n):N(n){
        bit.resize(N+1,0);
    }
    void add(int x,int a){
        for(x;x<=N;x+=(x&-x)) bit[x]+=a;
    }
    ll sum(int x){
        ll ret=0;
        for(x;x>0;x-=(x&-x)) ret+=bit[x];
        return ret;
    }
    ll lower_bound(ll X){
        if(sum(N)<X) return -1;
        ll ret=0,memo=1,sum=0;
        while(memo*2<=N) memo*=2;
        while(memo>0){
            if(memo+ret<=N&&sum+bit[memo+ret]<X){
                sum+=bit[memo+ret];
                ret+=memo;
            }
            memo/=2;
        }
        return ret+1;
    }
};
struct Union_Find{
    ll N;
    vi par;
    vi siz;
    Union_Find(int n):N(n){
        par.resize(N);
        siz.resize(N,1);
        rep(i,0,N) par[i]=i;
    }
    ll root(ll X){
        if(par[X]==X) return X;
        return par[X]=root(par[X]);
    }
    bool same(ll X,ll Y){
        return root(X)==root(Y);
    }
    void unite(ll X,ll Y){
        X=root(X);
        Y=root(Y);
        if(X==Y) return;
        par[X]=Y;
        siz[Y]+=siz[X];
        siz[X]=0;
    }
    ll size(ll X){
        return siz[root(X)];
    }
};
long long modpow(long long a, long long n, long long mod) {
    long long res = 1;
    while (n > 0) {
        if (n & 1) res = res * a % mod;
        a = a * a % mod;
        n >>= 1;
    }
    return res;
}
vi fac,finv,inv;
void COMinit() {
    fac.resize(MAX);
    finv.resize(MAX);
    inv.resize(MAX);
    fac[0] = fac[1] = 1;
    finv[0] = finv[1] = 1;
    inv[1] = 1;
    for (int i = 2; i < MAX; i++){
        fac[i] = fac[i - 1] * i % MOD;
        inv[i] = MOD - inv[MOD%i] * (MOD / i) % MOD;
        finv[i] = finv[i - 1] * inv[i] % MOD;
    }
}
ll COM(ll n,ll r){
    if(n<r||n<0||r<0) return 0;
    return fac[n]*finv[r]%MOD*finv[n-r]%MOD;
}
void comp(vi &A){
    std::map<ll,ll> mem;
    rep(i,0,A.size()) mem[A[i]]=0;
    ll cnt=0;
    for(auto &p:mem) p.second=cnt++;
    rep(i,0,A.size()) A[i]=mem[A[i]];
}
ll RLCS(string S){
    string T=S;
    reverse(ALL(T));
    ll N=S.size();
    vii dp(N+1,vi(N+1));
    REP(i,0,N){
        REP(j,0,N){
            if(!i){
                if(j) dp[i][j]=dp[i][j-1];
            }
            else if(!j){
                dp[i][j]=dp[i-1][j];
            }
            else{
                dp[i][j]=std::max(dp[i][j-1],dp[i-1][j]);
                if(S[i-1]==T[j-1]) dp[i][j]=std::max(dp[i][j],dp[i-1][j-1]+1);
            }
        }
    }
    return dp[N][N];
}
int main(){
    std::ios::sync_with_stdio(false);
    std::cin.tie(nullptr);
    string S; cin>>S;
    ll K,N=S.size(); cin>>K;
    string T=S; reverse(ALL(T));
    vector<vii> dp(N/2+1,vii(N/2+1,vi(K+1,INF)));
    dp[0][0][0]=0;
    vii mem(26);
    rep(i,0,N/2) mem[T[i]-'a'].pb(i+1);
    rep(i,0,N/2){
        REP(j,0,N/2){
            REP(k,0,K) dp[i+1][j][k]=dp[i][j][k];
        }
        rep(j,0,N/2){
            REP(k,0,K){
                if(dp[i][j][k]==INF) continue;
                ll X=disup(mem[S[i]-'a'],dp[i][j][k]);
                if(X<mem[S[i]-'a'].size()){
                    ll Y=mem[S[i]-'a'][X];
                    dp[i+1][j+1][k]=std::min(dp[i+1][j+1][k],Y);
                }
                if(dp[i][j][k]<N/2&&k<K){
                    dp[i+1][j+1][k+1]=std::min(dp[i+1][j+1][k+1],dp[i][j][k]+1);
                }
            }
        }
        REP(j,0,N/2){
            REP(k,1,K) dp[i+1][j][k]=std::min(dp[i+1][j][k],dp[i+1][j][k-1]);
        }
    }
    ll ans=0;
    per(i,N/2,0){
        ll cnt=0p
        per(j,N/2,0){
            if(dp[i][j][K]!=INF){
                ll left=i,right=N-1-dp[i][j][K];
                if(left<=right){
                    string P=S.substr(left,right-left+1);
                    ans=std::max(ans,j*2+RLCS(P));
                }
                else{
                    ans=std::max(ans,j*2);
                }
                cnt++;
                if(cnt==10) break;
            }
        }
    }
    cout<<ans<<endl;
}


Compiler output:
a.cc: In function 'int main()':
a.cc:215:16: error: unable to find numeric literal operator 'operator""p'
  215 |         ll cnt=0p
      |                ^~
a.cc:216:13: error: 'j' was not declared in this scope
  216 |         per(j,N/2,0){
      |             ^
a.cc:9:46: note: in definition of macro 'per'
    9 | #define per(i,j,n) for(ll i=(ll)(j);(ll)(n)<=i;i--)
      |                                              ^