Problem p03703 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <bitset>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
typedef long double ld;
const ll INF = 1e+14;
typedef pair<int, int> P;
#define stop                                                                   \
  char nyaa;                                                                   \
  cin >> nyaa;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(), c.end()
#define pb push_back

struct BIT {
private:
  vector<ll> node;
  int n;

public:
  BIT(int n_) {
    n = n_;
    node.resize(n + 1, 0);
  }
  void add(int i, ll x) {
    while (i <= n) {
      node[i] += x;
      i += i & -i;
    }
  }
  ll sum(int i) {
    ll ret = 0;
    while (i > 0) {
      ret += node[i];
      i -= i & -i;
    }
    return ret;
  }
  ll sum(int a, int b) { return sum(b) - sum(a - 1); }
};

void Yes() {
  cout << "Yes" << endl;
  exit(0);
}

void No() {
  cout << "No" << endl;
  exit(0);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int N;
  cin >> N;
  ll K;
  cin >> K;
  vector<ll> a(N), x(N + 1), y(N + 1);
  x[0] = 0;
  y[0] = 0;
  rep(i, N) {
    cin >> a[i];
    a[i] -= K;
    x[i + 1] = x[i] + a[i];
    y[i + 1] = x[i + 1];
  }
  sort(all(y));
  y.erase(unique(all(y)), y.end());
  map<ll, int> mp;
  rep(i, N + 1) mp[y[i]] = i;

  rep(i, N + 1) x[i] = mp[x[i]];

  BIT b(N + 1);
  ll ans = 0;
  rep(i, N + 1) {
    ans += b.sum(x[i]);
    b.add(x[i], 1);
  }

  cout << ans << endl;
  return 0;
}

Fixed submission:
#include <algorithm>
#include <bitset>
#include <ciso646>
#include <cmath>
#include <complex>
#include <cstdio>
#include <functional>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <random>
#include <set>
#include <stack>
#include <string>
#include <unordered_map>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
typedef unsigned int ui;
const ll mod = 1000000007;
typedef long double ld;
const ll INF = 1e+14;
typedef pair<int, int> P;
#define stop                                                                   \
  char nyaa;                                                                   \
  cin >> nyaa;
#define rep(i, n) for (int i = 0; i < n; i++)
#define per(i, n) for (int i = n - 1; i >= 0; i--)
#define Rep(i, sta, n) for (int i = sta; i < n; i++)
#define rep1(i, n) for (int i = 1; i <= n; i++)
#define per1(i, n) for (int i = n; i >= 1; i--)
#define Rep1(i, sta, n) for (int i = sta; i <= n; i++)
typedef complex<ld> Point;
const ld eps = 1e-8;
const ld pi = acos(-1.0);
typedef pair<ld, ld> LDP;
typedef pair<ll, ll> LP;
#define fr first
#define sc second
#define all(c) c.begin(), c.end()
#define pb push_back

struct BIT {
private:
  vector<ll> node;
  int n;

public:
  BIT(int n_) {
    n = n_;
    node.resize(n + 1, 0);
  }
  void add(int i, ll x) {
    while (i <= n) {
      node[i] += x;
      i += i & -i;
    }
  }
  ll sum(int i) {
    ll ret = 0;
    while (i > 0) {
      ret += node[i];
      i -= i & -i;
    }
    return ret;
  }
  ll sum(int a, int b) { return sum(b) - sum(a - 1); }
};

void Yes() {
  cout << "Yes" << endl;
  exit(0);
}

void No() {
  cout << "No" << endl;
  exit(0);
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);

  int N;
  cin >> N;
  ll K;
  cin >> K;
  vector<ll> a(N), x(N + 1), y(N + 1);
  x[0] = 0;
  y[0] = 0;
  rep(i, N) {
    cin >> a[i];
    a[i] -= K;
    x[i + 1] = x[i] + a[i];
    y[i + 1] = x[i + 1];
  }
  sort(all(y));
  y.erase(unique(all(y)), y.end());
  map<ll, int> mp;
  rep(i, N + 1) mp[y[i]] = i + 1;

  rep(i, N + 1) x[i] = mp[x[i]];

  BIT b(N + 1);
  ll ans = 0;
  rep(i, N + 1) {
    ans += b.sum(x[i]);
    b.add(x[i], 1);
  }

  cout << ans << endl;
  return 0;
}