Problem p03279 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
#define REP(i, k, n) for (long long i = k; i < (long long)(n); i++)
#define all(a) a.begin(), a.end()
#define pb push_back
#define eb emplace_back
#define lb(v, k) (lower_bound(all(v), k) - v.begin())
#define ub(v, k) (upper_bound(all(v), k) - v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T, vector<T>, greater<T>>
#define dame(a)                                                                \
  {                                                                            \
    out(a);                                                                    \
    return 0;                                                                  \
  }
#define decimal cout << fixed << setprecision(15);
#define dupli(a) erase(unique(all(a)))
typedef long long ll;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> PP;
typedef tuple<ll, ll, ll, ll> PPP;
typedef multiset<ll> S;
using vi = vector<ll>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vp = vector<P>;
using vvp = vector<vp>;
using vb = vector<bool>;
using vvb = vector<vb>;
const ll inf = 1001001001001001001;
const int INF = 1001001001;
const int mod = 1000000007;
const double eps = 1e-10;
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> void out(T a) { cout << a << '\n'; }
template <class T> void outp(T a) {
  cout << '(' << a.fi << ',' << a.se << ')' << '\n';
}
template <class T> void outvp(T v) {
  rep(i, v.size()) cout << '(' << v[i].fi << ',' << v[i].se << ')';
  cout << '\n';
}
template <class T> void outvvp(T v) { rep(i, v.size()) outvp(v[i]); }
template <class T> void outv(T v) {
  rep(i, v.size()) {
    if (i)
      cout << ' ';
    cout << v[i];
  }
  cout << '\n';
}
template <class T> void outvv(T v) { rep(i, v.size()) outv(v[i]); }
template <class T> bool isin(T x, T l, T r) { return (l) <= (x) && (x) <= (r); }
template <class T> void yesno(T b) {
  if (b)
    out("yes");
  else
    out("no");
}
template <class T> void YesNo(T b) {
  if (b)
    out("Yes");
  else
    out("No");
}
template <class T> void YESNO(T b) {
  if (b)
    out("YES");
  else
    out("NO");
}
template <class T> void noyes(T b) {
  if (b)
    out("no");
  else
    out("yes");
}
template <class T> void NoYes(T b) {
  if (b)
    out("No");
  else
    out("Yes");
}
template <class T> void NOYES(T b) {
  if (b)
    out("NO");
  else
    out("YES");
}
void outs(ll a, ll b) {
  if (a >= inf - 100)
    out(b);
  else
    out(a);
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll modpow(ll a, ll b) {
  a %= mod;
  if (b == 0)
    return 1;
  if (b & 1)
    return a * modpow(a, b - 1) % mod;
  ll k = modpow(a, b / 2);
  return k * k % mod;
}
vi seg;
ll N;
void init(ll n) {
  N = 1;
  while (N < n)
    N *= 2;
  seg = vi(N * 2 - 1);
}
void add(ll i, ll x) {
  i = N + i - 1;
  seg[i] += x;
  seg[i] %= mod;
  while (i > 0) {
    i = (i - 1) / 2;
    seg[i] = seg[i * 2 + 1] + seg[i * 2 + 2];
  }
}
ll getsum(ll a, ll b, ll k, ll l, ll r) {
  if (r <= a || b <= l)
    return 0;
  if (a <= l && r <= b)
    return seg[k];
  ll c1 = getsum(a, b, k * 2 + 1, l, (l + r) / 2);
  ll c2 = getsum(a, b, k * 2 + 2, (l + r) / 2, r);
  return c1 + c2;
}
int main() {
  ll n, m;
  cin >> n >> m;
  vi x(n), y(m);
  rep(i, n) cin >> x[i];
  rep(i, m) cin >> y[i];
  vp s;
  rep(i, n) {
    if (x[i] < y[0] || x[i] > y[m - 1])
      continue;
    ll k = lb(y, x[i]);
    s.eb(y[k] - x[i], y[k - 1] - x[i]);
  }
  sort(all(s));
  // outvp(s);
  vp ss;
  ss.pb(s[0]);
  rep(i, s.size() - 1) if (s[i + 1] != ss.back()) ss.pb(s[i + 1]);
  s = ss;
  // utvp(s);
  n = s.size();
  vi v(n);
  rep(i, n) v[i] = -s[i].se;
  vi t = v;
  sort(all(t));
  // outv(v);
  vi id(n);
  rep(i, n) id[i] = lb(t, v[i]) + 1;
  // outv(id);
  init(t.size() + 1);
  add(0, 1);
  rep(i, n) {
    add(id[i], getsum(0, id[i], 0, 0, N) % mod);
    // outv(seg);
  }
  out(getsum(0, N, 0, 0, N) % mod);
}

Fixed submission:
#include <bits/stdc++.h>
using namespace std;
#define rep(i, n) for (long long i = 0; i < (long long)(n); i++)
#define REP(i, k, n) for (long long i = k; i < (long long)(n); i++)
#define all(a) a.begin(), a.end()
#define pb push_back
#define eb emplace_back
#define lb(v, k) (lower_bound(all(v), k) - v.begin())
#define ub(v, k) (upper_bound(all(v), k) - v.begin())
#define fi first
#define se second
#define pi M_PI
#define PQ(T) priority_queue<T>
#define SPQ(T) priority_queue<T, vector<T>, greater<T>>
#define dame(a)                                                                \
  {                                                                            \
    out(a);                                                                    \
    return 0;                                                                  \
  }
#define decimal cout << fixed << setprecision(15);
#define dupli(a) erase(unique(all(a)))
typedef long long ll;
typedef pair<ll, ll> P;
typedef tuple<ll, ll, ll> PP;
typedef tuple<ll, ll, ll, ll> PPP;
typedef multiset<ll> S;
using vi = vector<ll>;
using vvi = vector<vi>;
using vvvi = vector<vvi>;
using vp = vector<P>;
using vvp = vector<vp>;
using vb = vector<bool>;
using vvb = vector<vb>;
const ll inf = 1001001001001001001;
const int INF = 1001001001;
const int mod = 1000000007;
const double eps = 1e-10;
template <class T> bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> void out(T a) { cout << a << '\n'; }
template <class T> void outp(T a) {
  cout << '(' << a.fi << ',' << a.se << ')' << '\n';
}
template <class T> void outvp(T v) {
  rep(i, v.size()) cout << '(' << v[i].fi << ',' << v[i].se << ')';
  cout << '\n';
}
template <class T> void outvvp(T v) { rep(i, v.size()) outvp(v[i]); }
template <class T> void outv(T v) {
  rep(i, v.size()) {
    if (i)
      cout << ' ';
    cout << v[i];
  }
  cout << '\n';
}
template <class T> void outvv(T v) { rep(i, v.size()) outv(v[i]); }
template <class T> bool isin(T x, T l, T r) { return (l) <= (x) && (x) <= (r); }
template <class T> void yesno(T b) {
  if (b)
    out("yes");
  else
    out("no");
}
template <class T> void YesNo(T b) {
  if (b)
    out("Yes");
  else
    out("No");
}
template <class T> void YESNO(T b) {
  if (b)
    out("YES");
  else
    out("NO");
}
template <class T> void noyes(T b) {
  if (b)
    out("no");
  else
    out("yes");
}
template <class T> void NoYes(T b) {
  if (b)
    out("No");
  else
    out("Yes");
}
template <class T> void NOYES(T b) {
  if (b)
    out("NO");
  else
    out("YES");
}
void outs(ll a, ll b) {
  if (a >= inf - 100)
    out(b);
  else
    out(a);
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  return gcd(b, a % b);
}
ll modpow(ll a, ll b) {
  a %= mod;
  if (b == 0)
    return 1;
  if (b & 1)
    return a * modpow(a, b - 1) % mod;
  ll k = modpow(a, b / 2);
  return k * k % mod;
}
vi seg;
ll N;
void init(ll n) {
  N = 1;
  while (N < n)
    N *= 2;
  seg = vi(N * 2 - 1);
}
void add(ll i, ll x) {
  i = N + i - 1;
  seg[i] += x;
  seg[i] %= mod;
  while (i > 0) {
    i = (i - 1) / 2;
    seg[i] = seg[i * 2 + 1] + seg[i * 2 + 2];
  }
}
ll getsum(ll a, ll b, ll k, ll l, ll r) {
  if (r <= a || b <= l)
    return 0;
  if (a <= l && r <= b)
    return seg[k];
  ll c1 = getsum(a, b, k * 2 + 1, l, (l + r) / 2);
  ll c2 = getsum(a, b, k * 2 + 2, (l + r) / 2, r);
  return c1 + c2;
}
int main() {
  ll n, m;
  cin >> n >> m;
  vi x(n), y(m);
  rep(i, n) cin >> x[i];
  rep(i, m) cin >> y[i];
  vp s;
  rep(i, n) {
    if (x[i] < y[0] || x[i] > y[m - 1])
      continue;
    ll k = lb(y, x[i]);
    s.eb(y[k] - x[i], y[k - 1] - x[i]);
  }
  sort(all(s));
  if (s.size() == 0)
    dame(1);
  // outvp(s);
  vp ss;
  ss.pb(s[0]);
  rep(i, s.size() - 1) if (s[i + 1] != ss.back()) ss.pb(s[i + 1]);
  s = ss;
  // utvp(s);
  n = s.size();
  vi v(n);
  rep(i, n) v[i] = -s[i].se;
  vi t = v;
  sort(all(t));
  // outv(v);
  vi id(n);
  rep(i, n) id[i] = lb(t, v[i]) + 1;
  // outv(id);
  init(t.size() + 1);
  add(0, 1);
  rep(i, n) {
    add(id[i], getsum(0, id[i], 0, 0, N) % mod);
    // outv(seg);
  }
  out(getsum(0, N, 0, 0, N) % mod);
}