Problem p03686 (C++)

Buggy submission (status: Runtime Error):
#include "bits/stdc++.h"

#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (int x = (l); x <= (u); x++)
#define RREP(x, l, u) for (int x = (l); x >= (u); x--)
#define mst(x, a) memset(x, a, sizeof(x))
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define se second
#define fi first
#define dbg(x) cout << #x << " = " << (x) << endl;
#define sz(x) ((int)x.size())
#define cl(x) x.clear()

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;

const int maxn = 100010;
const int mod = 1e9 + 7;
const int MAX = 1000000010;
const double eps = 1e-6;
const double PI = acos(-1);

template <typename T> inline void read(T &x) {
  x = 0;
  T f = 1;
  char ch;
  do {
    ch = getchar();
    if (ch == '-')
      f = -1;
  } while (ch < '0' || ch > '9');
  do
    x = x * 10 + ch - '0', ch = getchar();
  while (ch <= '9' && ch >= '0');
  x *= f;
}

template <typename A, typename B> inline void read(A &x, B &y) {
  read(x);
  read(y);
}
template <typename A, typename B, typename C>
inline void read(A &x, B &y, C &z) {
  read(x);
  read(y);
  read(z);
}
template <typename A, typename B, typename C, typename D>
inline void read(A &x, B &y, C &z, D &w) {
  read(x);
  read(y);
  read(z);
  read(w);
}
template <typename A, typename B> inline A fexp(A x, B p) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mod)
    if (p & 1)
      ans = 1LL * ans * x % mod;
  return ans;
}
template <typename A, typename B> inline A fexp(A x, B p, A mo) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mo)
    if (p & 1)
      ans = 1LL * ans * x % mo;
  return ans;
}

int n, m, ans;

vector<int> has[maxn];

struct Node {
  int l, r, mx, bj;
} T[maxn << 2];

void pushdown(int i) {
  if (!T[i].bj)
    return;
  T[i << 1].mx += T[i].bj;
  T[i << 1].bj += T[i].bj;
  T[i << 1 | 1].mx += T[i].bj;
  T[i << 1 | 1].bj += T[i].bj;
  T[i].bj = 0;
}

void build(int i, int l, int r) {
  T[i].l = l;
  T[i].r = r;
  if (l == r) {
    T[i].mx = l;
    return;
  }
  int M = l + r >> 1;
  build(i << 1, l, M);
  build(i << 1 | 1, M + 1, r);
  T[i].mx = max(T[i << 1].mx, T[i << 1 | 1].mx);
}

void update(int i, int l, int r) {
  if (l <= T[i].l && T[i].r <= r) {
    T[i].mx++;
    T[i].bj++;
    return;
  }
  pushdown(i);
  int M = T[i].l + T[i].r >> 1;
  if (l <= M)
    update(i << 1, l, r);
  if (r > M)
    update(i << 1 | 1, l, r);
  T[i].mx = max(T[i << 1].mx, T[i << 1 | 1].mx);
}

void Work() {
  ans = n - m;
  REP(i, 0, m + 1) {
    for (auto x : has[i])
      update(1, 1, x);
    ans = max(ans, T[1].mx - i - m - 1);
  }
  iout(ans);
}

void Init() {
  read(n, m);
  REP(i, 1, n) {
    int x, y;
    read(x, y);
    has[x].PB(y);
  }
  build(1, 0, m + 1);
}

int main() {
  Init();
  Work();
  return 0;
}


Fixed submission:
#include "bits/stdc++.h"

#define PB push_back
#define PF push_front
#define LB lower_bound
#define UB upper_bound
#define fr(x) freopen(x, "r", stdin)
#define fw(x) freopen(x, "w", stdout)
#define iout(x) printf("%d\n", x)
#define lout(x) printf("%lld\n", x)
#define REP(x, l, u) for (int x = (l); x <= (u); x++)
#define RREP(x, l, u) for (int x = (l); x >= (u); x--)
#define mst(x, a) memset(x, a, sizeof(x))
#define PII pair<int, int>
#define PLL pair<ll, ll>
#define MP make_pair
#define se second
#define fi first
#define dbg(x) cout << #x << " = " << (x) << endl;
#define sz(x) ((int)x.size())
#define cl(x) x.clear()

typedef long long ll;
typedef unsigned long long ull;
typedef double db;
typedef long double ld;
using namespace std;

const int maxn = 200010;
const int mod = 1e9 + 7;
const int MAX = 1000000010;
const double eps = 1e-6;
const double PI = acos(-1);

template <typename T> inline void read(T &x) {
  x = 0;
  T f = 1;
  char ch;
  do {
    ch = getchar();
    if (ch == '-')
      f = -1;
  } while (ch < '0' || ch > '9');
  do
    x = x * 10 + ch - '0', ch = getchar();
  while (ch <= '9' && ch >= '0');
  x *= f;
}

template <typename A, typename B> inline void read(A &x, B &y) {
  read(x);
  read(y);
}
template <typename A, typename B, typename C>
inline void read(A &x, B &y, C &z) {
  read(x);
  read(y);
  read(z);
}
template <typename A, typename B, typename C, typename D>
inline void read(A &x, B &y, C &z, D &w) {
  read(x);
  read(y);
  read(z);
  read(w);
}
template <typename A, typename B> inline A fexp(A x, B p) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mod)
    if (p & 1)
      ans = 1LL * ans * x % mod;
  return ans;
}
template <typename A, typename B> inline A fexp(A x, B p, A mo) {
  A ans = 1;
  for (; p; p >>= 1, x = 1LL * x * x % mo)
    if (p & 1)
      ans = 1LL * ans * x % mo;
  return ans;
}

int n, m, ans;

vector<int> has[maxn];

struct Node {
  int l, r, mx, bj;
} T[maxn << 2];

void pushdown(int i) {
  if (!T[i].bj)
    return;
  T[i << 1].mx += T[i].bj;
  T[i << 1].bj += T[i].bj;
  T[i << 1 | 1].mx += T[i].bj;
  T[i << 1 | 1].bj += T[i].bj;
  T[i].bj = 0;
}

void build(int i, int l, int r) {
  T[i].l = l;
  T[i].r = r;
  if (l == r) {
    T[i].mx = l;
    return;
  }
  int M = l + r >> 1;
  build(i << 1, l, M);
  build(i << 1 | 1, M + 1, r);
  T[i].mx = max(T[i << 1].mx, T[i << 1 | 1].mx);
}

void update(int i, int l, int r) {
  if (l <= T[i].l && T[i].r <= r) {
    T[i].mx++;
    T[i].bj++;
    return;
  }
  pushdown(i);
  int M = T[i].l + T[i].r >> 1;
  if (l <= M)
    update(i << 1, l, r);
  if (r > M)
    update(i << 1 | 1, l, r);
  T[i].mx = max(T[i << 1].mx, T[i << 1 | 1].mx);
}

void Work() {
  ans = n - m;
  REP(i, 0, m + 1) {
    for (auto x : has[i])
      update(1, 1, x);
    ans = max(ans, T[1].mx - i - m - 1);
  }
  iout(ans);
}

void Init() {
  read(n, m);
  REP(i, 1, n) {
    int x, y;
    read(x, y);
    has[x].PB(y);
  }
  build(1, 0, m + 1);
}

int main() {
  Init();
  Work();
  return 0;
}