Problem p02626 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<P, ll> T;
typedef pair<long double, ll> Ps;
typedef pair<ll, bool> Pb;

const ll INF = 1e18;
const ll fact_table = 3200008;
long double Pi = 3.1415926535897932384626;

priority_queue<ll> pql;
priority_queue<P> pqp;
priority_queue<P> bag;
// big priority queue
priority_queue<ll, vector<ll>, greater<ll>> pqls;
priority_queue<P, vector<P>, greater<P>> pqps;
// small priority queue
// top pop

ll dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
ll dy[8] = {0, 1, 0, -1, 1, -1, -1, 1};
char dir[] = "DRUL";
// ↓,→,↑,←

/*
#define endl "\\n"
#ifdef ENJAPMA
#undef endl
#endif
*/
#define p(x) cout << x << endl;
#define el cout << endl;
#define pe(x) cout << x << " ";
#define ps(x) cout << fixed << setprecision(25) << x << endl;
#define pu(x) cout << (x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)();
#define pc(x) cout << x << ",";
#define rep(i, n) for (ll i = 0; i < (n); i++)

// const ll mod = 998244353ll;
const ll mod = 1000000007ll;

ll mypow(ll a, ll b, ll mod) {
  ll x = 1;
  while (b) {
    while (!(b & 1)) {
      (a *= a) %= mod;
      b >>= 1;
    }
    (x *= a) %= mod;
    b--;
  }
  return x;
}
void YES(bool cond) {
  if (cond) {
    p("YES");
  } else {
    p("NO");
  }
  return;
}
void Yes(bool cond) {
  if (cond) {
    p("Yes");
  } else {
    p("No");
  }
  return;
}
void line() {
  p("--------------------");
  return;
}

ll fact[fact_table + 5], rfact[fact_table + 5];

void c3_init() {
  fact[0] = rfact[0] = 1;
  for (ll i = 1; i <= fact_table; i++) {
    fact[i] = (fact[i - 1] * i) % mod;
  }
  rfact[fact_table] = mypow(fact[fact_table], mod - 2, mod);
  for (ll i = fact_table; i >= 1; i--) {
    rfact[i - 1] = rfact[i] * i;
    rfact[i - 1] %= mod;
  }
  return;
}
ll c3(ll n, ll r) {
  return (((fact[n] * rfact[r]) % mod) * rfact[n - r]) % mod;
}

bool multicase = false;

ll n, m, k, num, a, b, c, d, e, h, q, ans, sum;

typedef vector<ll> vec;
typedef vector<vector<ll>> mat;

ll x[5005];
bool used[5005], used2[5005];

string s, t;

void solve() {
  cin >> n;
  ll sum = 0;
  for (ll i = 0; i < n; i++) {
    cin >> x[i];
    if (i > 1)
      sum ^= x[i];
  }
  ll a = x[0], b = x[1];

  // (a - i) ^ (b + i) == sum　となるような最小のi

  vec bit;

  for (ll i = 0; i < 60; i++) {
    if (!((1ll << i) & sum)) {
      used[i] = true;
    }
  }

  ll aim_sum = a + b - sum;

  bool dame = false;
  if (aim_sum % 2 == 1)
    dame = true;

  aim_sum /= 2;

  if (aim_sum < 0)
    dame = true;
  if (aim_sum > a)
    dame = true;

  for (ll i = 0; i < 60; i++) {
    if ((aim_sum & (1ll << i)) && (sum & (1ll << i)))
      dame = true;
  }

  ll now_a = aim_sum;

  for (ll i = 59; i >= 0; i--) {
    if (sum & (1ll << i)) {
      if (now_a + (1ll << i) <= a) {
        now_a += (1ll << i);
      }
    }
  }

  if (a - now_a == x[0])
    dame = true;

  if (dame) {
    p(-1);
  } else {
    p(a - now_a);
  }

  return;
}

int main() {
  // init();
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll q, testcase = 1;
  if (multicase) {
    cin >> q;
  } else {
    q = 1;
  }
  while (q--) {
    // pu("Case ");pu("#");pu(testcase);pu(": ");
    solve();
    testcase++;
  }
  // solve();
  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
#include <stdlib.h>
#include <sys/time.h>
#include <unistd.h>

using namespace std;

typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<P, ll> T;
typedef pair<long double, ll> Ps;
typedef pair<ll, bool> Pb;

const ll INF = 1e18;
const ll fact_table = 3200008;
long double Pi = 3.1415926535897932384626;

priority_queue<ll> pql;
priority_queue<P> pqp;
priority_queue<P> bag;
// big priority queue
priority_queue<ll, vector<ll>, greater<ll>> pqls;
priority_queue<P, vector<P>, greater<P>> pqps;
// small priority queue
// top pop

ll dx[8] = {1, 0, -1, 0, 1, 1, -1, -1};
ll dy[8] = {0, 1, 0, -1, 1, -1, -1, 1};
char dir[] = "DRUL";
// ↓,→,↑,←

/*
#define endl "\\n"
#ifdef ENJAPMA
#undef endl
#endif
*/
#define p(x) cout << x << endl;
#define el cout << endl;
#define pe(x) cout << x << " ";
#define ps(x) cout << fixed << setprecision(25) << x << endl;
#define pu(x) cout << (x);
#define pb push_back
#define lb lower_bound
#define ub upper_bound
#define CLEAR(a) a = decltype(a)();
#define pc(x) cout << x << ",";
#define rep(i, n) for (ll i = 0; i < (n); i++)

// const ll mod = 998244353ll;
const ll mod = 1000000007ll;

ll mypow(ll a, ll b, ll mod) {
  ll x = 1;
  while (b) {
    while (!(b & 1)) {
      (a *= a) %= mod;
      b >>= 1;
    }
    (x *= a) %= mod;
    b--;
  }
  return x;
}
void YES(bool cond) {
  if (cond) {
    p("YES");
  } else {
    p("NO");
  }
  return;
}
void Yes(bool cond) {
  if (cond) {
    p("Yes");
  } else {
    p("No");
  }
  return;
}
void line() {
  p("--------------------");
  return;
}

ll fact[fact_table + 5], rfact[fact_table + 5];

void c3_init() {
  fact[0] = rfact[0] = 1;
  for (ll i = 1; i <= fact_table; i++) {
    fact[i] = (fact[i - 1] * i) % mod;
  }
  rfact[fact_table] = mypow(fact[fact_table], mod - 2, mod);
  for (ll i = fact_table; i >= 1; i--) {
    rfact[i - 1] = rfact[i] * i;
    rfact[i - 1] %= mod;
  }
  return;
}
ll c3(ll n, ll r) {
  return (((fact[n] * rfact[r]) % mod) * rfact[n - r]) % mod;
}

bool multicase = false;

ll n, m, k, num, a, b, c, d, e, h, q, ans, sum;

typedef vector<ll> vec;
typedef vector<vector<ll>> mat;

ll x[5005];

string s, t;

void solve() {
  cin >> n;
  ll sum = 0;
  for (ll i = 0; i < n; i++) {
    cin >> x[i];
    sum ^= x[i];
  }
  for (ll i = 0; i < x[0]; i++) {
    x[0] -= i;
    x[1] += i;
    ll sum = 0;
    for (ll j = 0; j < n; j++) {
      sum ^= x[j];
    }
    if (sum == 0) {
      p(i);
      return;
    }
    x[0] += i;
    x[1] -= i;
  }
  p(-1);
  return;
}

int main() {
  // init();
  ios::sync_with_stdio(false);
  cin.tie(nullptr);
  ll q, testcase = 1;
  if (multicase) {
    cin >> q;
  } else {
    q = 1;
  }
  while (q--) {
    // pu("Case ");pu("#");pu(testcase);pu(": ");
    solve();
    testcase++;
  }
  // solve();
  return 0;
}