Longest palindrome

input/code.cpp: In function 'void solve()':
input/code.cpp:60:20: warning: statement has no effect [-Wunused-value]
   60 | #define debug(...) 42
      |                    ^~
input/code.cpp:95:5: note: in expansion of macro 'debug'
   95 |     debug(p);
      |     ^~~~~
input/code.cpp:60:20: warning: statement has no effect [-Wunused-value]
   60 | #define debug(...) 42
      |                    ^~
input/code.cpp:106:5: note: in expansion of macro 'debug'
  106 |     debug(ans, pos);
      |     ^~~~~

#pragma GCC optimize("O3","unroll-loops")
#pragma GCC target("avx2,bmi,bmi2,popcnt,lzcnt")

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

#define int long long
#define rep(i, a, b) for(int i = a; i < (b); ++i)
#define all(x) begin(x), end(x)
#define sz(x) (int)(x).size()
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vi;

string to_string(string s) {
    return '"' + s + '"';
}
 
string to_string(const char* s) {
    return to_string((string) s);
}
 
string to_string(bool b) {
    return (b ? "true" : "false");
}
 
template <typename A, typename B>
string to_string(pair<A, B> p) {
    return "(" + to_string(p.first) + ", " + to_string(p.second) + ")";
}
 
template <typename A>
string to_string(A v) {
    bool first = true;
    string res = "{";
    for (const auto &x : v) {
        if (!first) {
            res += ", ";
        }
        first = false;
        res += to_string(x);
    }
    res += "}";
    return res;
}
 
void debug_out() {
    cerr << endl;
}
 
template <typename Head, typename... Tail>
void debug_out(Head H, Tail... T) {
    cerr << " " << to_string(H);
    debug_out(T...);
}
 
#ifdef LOCAL
#define debug(...) cerr << "[" << #__VA_ARGS__ << "]:", debug_out(__VA_ARGS__)
#else
#define debug(...) 42
#endif

/**
 * Author: User adamant on CodeForces
 * Source: http://codeforces.com/blog/entry/12143
 * Description: For each position in a string, computes p[0][i] = half length of
 *  longest even palindrome around pos i, p[1][i] = longest odd (half rounded down).
 * Time: O(N)
 * Status: Stress-tested
 */

array<vi, 2> manacher(const string& s) {
    int n = sz(s);
    array<vi,2> p = {vi(n+1), vi(n)};
    rep(z,0,2) for (int i=0,l=0,r=0; i < n; i++) {
        int t = r-i+!z;
        if (i<r) p[z][i] = min(t, p[z][l+t]);
        int L = i-p[z][i], R = i+p[z][i]-!z;
        while (L>=1 && R+1<n && s[L-1] == s[R+1])
            p[z][i]++, L--, R++;
        if (R>r) l=L, r=R;
    }
    return p;
}

string s;
int n;

void solve() {
    cin >> s;
    n = sz(s);

    int ans = 0, pos = 0;
    auto p = manacher(s);
    debug(p);
    for (int i = 0; i < n; i++) {
        if (p[0][i] * 2 > ans) {
            ans = p[0][i] * 2;
            pos = i;
        }
        if (p[1][i] * 2 + 1 > ans) {
            ans = p[1][i] * 2 + 1;
            pos = i;
        }
    }
    debug(ans, pos);
    if (ans & 1) {
        int half = ans / 2;
        cout << s.substr(pos - half, ans);
    } else {
        int half = ans / 2;
        cout << s.substr(pos - half, ans);    
    }
}

signed main() {
    cin.tie(0)->sync_with_stdio(0);
    cin.exceptions(cin.failbit); // RTE if input wrong datatype

    solve();
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED