Problem p01879 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string.h>
#include <string>
#include <vector>
#define fi first
#define se second
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define gep(i, g, j) for (int i = g.head[j]; i != -1; i = g.e[i].next)
#define each(it, c)                                                            \\
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); it++)
#define rng(a) a.begin(), a.end()
#define maxs(x, y) x = max(x, y)
#define mins(x, y) x = min(x, y)
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcount
#define snuke srand((unsigned)clock() + (unsigned)time(NULL));
#define df(x) int x = in()
#define dame                                                                   \\
  {                                                                            \\
    puts("0");                                                                 \\
    return 0;                                                                  \\
  }
#define show(x) cout << #x << " = " << x << endl;
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
inline int in() {
  int x;
  scanf("%d", &x);
  return x;
}
inline void priv(vi a) {
  rep(i, sz(a)) printf("%d%c", a[i], i == sz(a) - 1 ? '\\n' : ' ');
}
template <typename T> istream &operator>>(istream &i, vector<T> &v) {
  rep(j, sz(v)) i >> v[j];
  return i;
}
template <typename T> string join(vector<T> &v) {
  stringstream s;
  rep(i, sz(v)) s << ' ' << v[i];
  return s.str().substr(1);
}
template <typename T> ostream &operator<<(ostream &o, vector<T> &v) {
  if (sz(v))
    o << join(v);
  return o;
}
template <typename T1, typename T2>
istream &operator>>(istream &i, pair<T1, T2> &v) {
  return i >> v.fi >> v.se;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &o, pair<T1, T2> &v) {
  return o << v.fi << "," << v.se;
}

const int MX = 100005, INF = 1001001001;
const ll LINF = 1e18;
const double eps = 1e-10;

const int D = 300, E = 351;
// Binary Indexed Tree
struct bit {
  typedef int TT;
  vector<TT> d;
  int n, hi;
  vi hist;
  bit() {}
  bit(int mx) : n(mx), d(mx), hist(MX), hi(0) {}
  void add(int i, TT x = 1) {
    for (++i; i < n; i += i & -i) {
      d[i] += x;
    }
  }
  void add2(int i, TT x = 1) {
    for (++i; i < n; i += i & -i) {
      hist[hi++] = i;
      d[i] += x;
    }
  }
  TT sum(int i) {
    TT x = 0;
    for (++i; i; i -= i & -i)
      x += d[i];
    return x;
  }
  void rev() { d = vi(n); }
  void rev2() {
    while (hi--)
      d[hist[hi]] = 0;
    hi = 0;
  }
};
//

int n, a[MX];
ll dl[E][MX], dr[E][MX];

int main() {
  // preprocess
  scanf("%d", &n);
  rep(i, n) scanf("%d", &a[i]), a[i] = n - a[i];
  bit t(n + 2);
  for (int i = 0; i <= n; i += D) {
    int di = i / D;
    ll sum = 0;
    for (int j = i; j < n; ++j) {
      sum += t.sum(a[j]);
      dl[di][j] = sum;
      t.add(a[j]);
    }
    t.rev();
    sum = 0;
    for (int j = i - 1; j >= 0; --j) {
      sum += t.sum(n - a[j]);
      dr[di][j] = sum;
      t.add(n - a[j]);
    }
    t.rev();
  }

  // online query
  int q;
  scanf("%d", &q);
  rep(qi, q) {
    int l, r;
    scanf("%d%d", &l, &r);
    --l;
    ll ans = 0;
    if (r - l <= D) {
      for (int i = l; i < r; ++i) {
        ans += t.sum(a[i]);
        t.add2(a[i]);
      }
      t.rev2();
    } else {
      int li = l / D + 1, ri = r / D;
      ans += dl[li][r - 1];
      ans += dr[ri][l];
      ans -= dl[li][ri * D - 1];
      vi p;
      for (int i = li * D - 1; i >= l; --i)
        p.pb(a[i] << 1);
      for (int i = ri * D; i < r; ++i)
        p.pb(a[i] << 1 | 1);
      sort(rng(p));
      int s = 0;
      for (int np : p) {
        if (np & 1)
          ans += s;
        else
          s++;
      }
    }
    printf("%lld\\n", ans);
  }
  return 0;
}

Error: TLE

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string.h>
#include <string>
#include <vector>
#define fi first
#define se second
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define gep(i, g, j) for (int i = g.head[j]; i != -1; i = g.e[i].next)
#define each(it, c)                                                            \\
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); it++)
#define rng(a) a.begin(), a.end()
#define maxs(x, y) x = max(x, y)
#define mins(x, y) x = min(x, y)
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcount
#define snuke srand((unsigned)clock() + (unsigned)time(NULL));
#define df(x) int x = in()
#define dame                                                                   \\
  {                                                                            \\
    puts("0");                                                                 \\
    return 0;                                                                  \\
  }
#define show(x) cout << #x << " = " << x << endl;
using namespace std;
typedef long long int ll;
typedef pair<int, int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
inline int in() {
  int x;
  scanf("%d", &x);
  return x;
}
inline void priv(vi a) {
  rep(i, sz(a)) printf("%d%c", a[i], i == sz(a) - 1 ? '\\n' : ' ');
}
template <typename T> istream &operator>>(istream &i, vector<T> &v) {
  rep(j, sz(v)) i >> v[j];
  return i;
}
template <typename T> string join(vector<T> &v) {
  stringstream s;
  rep(i, sz(v)) s << ' ' << v[i];
  return s.str().substr(1);
}
template <typename T> ostream &operator<<(ostream &o, vector<T> &v) {
  if (sz(v))
    o << join(v);
  return o;
}
template <typename T1, typename T2>
istream &operator>>(istream &i, pair<T1, T2> &v) {
  return i >> v.fi >> v.se;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &o, pair<T1, T2> &v) {
  return o << v.fi << "," << v.se;
}

const int MX = 100005, INF = 1001001001;
const ll LINF = 1e18;
const double eps = 1e-10;

const int D = 300, E = 351;
// Binary Indexed Tree
struct bit {
  typedef int TT;
  vector<TT> d;
  int n, hi;
  vi hist;
  bit() {}
  bit(int mx) : n(mx), d(mx), hist(MX * 20), hi(0) {}
  void add(int i, TT x = 1) {
    for (++i; i < n; i += i & -i) {
      hist[hi++] = i;
      d[i] += x;
    }
  }
  TT sum(int i) {
    TT x = 0;
    for (++i; i; i -= i & -i)
      x += d[i];
    return x;
  }
  void rev() {
    while (hi--)
      d[hist[hi]] = 0;
    hi = 0;
  }
};
//

int n, a[MX];
ll dl[E][MX], dr[E][MX];

int main() {
  // preprocess
  scanf("%d", &n);
  rep(i, n) scanf("%d", &a[i]), a[i] = n - a[i];
  bit t(n + 2);
  for (int i = 0; i <= n; i += D) {
    int di = i / D;
    ll sum = 0;
    for (int j = i; j < n; ++j) {
      sum += t.sum(a[j]);
      dl[di][j] = sum;
      t.add(a[j]);
    }
    t.rev();
    sum = 0;
    for (int j = i - 1; j >= 0; --j) {
      sum += t.sum(n - a[j]);
      dr[di][j] = sum;
      t.add(n - a[j]);
    }
    t.rev();
  }

  // online query
  int q;
  scanf("%d", &q);
  rep(qi, q) {
    int l, r;
    scanf("%d%d", &l, &r);
    --l;
    ll ans = 0;
    if (r - l <= D) {
      for (int i = l; i < r; ++i) {
        ans += t.sum(a[i]);
        t.add(a[i]);
      }
      t.rev();
    } else {
      int li = l / D + 1, ri = r / D;
      ans += dl[li][r - 1];
      ans += dr[ri][l];
      ans -= dl[li][ri * D - 1];
      vi p;
      for (int i = li * D - 1; i >= l; --i)
        p.pb(a[i] << 1);
      for (int i = ri * D; i < r; ++i)
        p.pb(a[i] << 1 | 1);
      sort(rng(p));
      int s = 0;
      for (int np : p) {
        if (np & 1)
          ans += s;
        else
          s++;
      }
    }
    printf("%lld\\n", ans);
  }
  return 0;
}