Problem p03802 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define sqr(x) ((x) * (x))
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define ld long double
#define vi vector<int>
#define HEAP(...) priority_queue<__VA_ARGS__>
#define heap(...)                                                              \
  priority_queue<__VA_ARGS__, vector<__VA_ARGS__>, greater<__VA_ARGS__>>
#define pii pair<int, int>
#define pb push_back
#define mp make_pair
#define debuge cerr << "isok" << endl
#define debug(x) cerr << #x << "=" << x << endl
#define dprintf(...) fprintf(stderr, __VA_ARGS__)
#define SS second
#define FF first
#define ls (k << 1)
#define rs (k << 1 | 1)
#define clr(a, x) memset(a, x, sizeof(a))
#define cpy(a, x) memcpy(a, x, sizeof(a))
#define file(x) freopen(x ".in", "r", stdin), freopen(x ".out", "w", stdout)
#define SZ(x) ((int)x.size())
using namespace std;
template <class T> inline void gmin(T &x, const T &y) {
  if (x > y)
    x = y;
}
template <class T> inline void gmax(T &x, const T &y) {
  if (x < y)
    x = y;
}
const int BufferSize = 1 << 16;
char buffer[BufferSize], *Bufferhead, *Buffertail;
bool Terminal;
inline char Getchar() {
  if (Bufferhead == Buffertail) {
    int l = fread(buffer, 1, BufferSize, stdin);
    if (!l) {
      Terminal = 1;
      return 0;
    }
    Buffertail = (Bufferhead = buffer) + l;
  }
  return *Bufferhead++;
}
template <class T> inline bool read(T &x) {
  x = 0;
  char c = Getchar(), rev = 0;
  while (c < '0' || c > '9') {
    c = Getchar();
    rev |= c == '-';
    if (Terminal)
      return 0;
  }
  while (c >= '0' && c <= '9')
    x = x * 10 + c - '0', c = Getchar();
  if (c == '.') {
    c = Getchar();
    double t = 0.1;
    while (c >= '0' && c <= '9')
      x = x + (c - '0') * t, c = Getchar(), t = t / 10;
  }
  x = rev ? -x : x;
  return 1;
}
template <class T1, class T2> inline bool read(T1 &x, T2 &y) {
  return read(x) & read(y);
}
template <class T1, class T2, class T3> inline bool read(T1 &x, T2 &y, T3 &z) {
  return read(x) & read(y) & read(z);
}
template <class T1, class T2, class T3, class T4>
inline bool read(T1 &x, T2 &y, T3 &z, T4 &w) {
  return read(x) & read(y) & read(z) & read(w);
}
inline bool reads(char *x) {
  char c = Getchar();
  while (c < 33 || c > 126) {
    c = Getchar();
    if (Terminal)
      return 0;
  }
  while (c >= 33 && c <= 126)
    (*x++) = c, c = Getchar();
  *x = 0;
  return 1;
}
template <class T> inline void print(T x, const char c = '\n') {
  if (!x) {
    putchar('0');
    putchar(c);
    return;
  }
  if (x < 0)
    putchar('-'), x = -x;
  int m = 0, a[20];
  while (x)
    a[m++] = x % 10, x /= 10;
  while (m--)
    putchar(a[m] + '0');
  putchar(c);
}
//--------------------------------head---------------------------------------------

const int N = 70005, M = 100005, mod = 1e9 + 7;
template <class T, class S> inline void ch(T &x, const S y) {
  x = (x + y) % mod;
}
inline int exp(int x, int y, const int mod = ::mod) {
  int ans = 1;
  while (y) {
    if (y & 1)
      ans = (ll)ans * x % mod;
    x = (ll)x * x % mod;
    y >>= 1;
  }
  return ans;
}

int n, m, inf, cnt, xx[N], yy[N], num[N][2], pp[N];
pii a[N];
int vis[N];
vi g[N], f[N], seq;

inline int pos(int x, int y = 0) {
  return lower_bound(a + 1, a + n * 2 + 1, mp(x, y)) - a;
}
void add(int x, int y) {
  g[x].pb(y);
  f[y].pb(x);
}
inline void build(int l, int r, int k) {
  if (l == r) {
    pp[l] = k;
    gmax(cnt, k);
    return;
  }
  int mid = l + r >> 1;
  build(l, mid, ls);
  build(mid + 1, r, rs);
  add(num[k][0], num[ls][0]);
  add(num[ls][1], num[k][1]);
  add(num[k][0], num[rs][0]);
  add(num[rs][1], num[k][1]);
}
inline void get(int l, int r, int x, int y, int k, int p) {
  if (x > y)
    return;
  if (x <= l && r <= y) {
    add(num[pp[p]][1], num[k][0]);
    add(num[k][1], num[pp[p]][0]);
    return;
  }
  int mid = l + r >> 1;
  if (x <= mid)
    get(l, mid, x, y, ls, p);
  if (y > mid)
    get(mid + 1, r, x, y, rs, p);
}
inline void pre(int x) {
  vis[x] = 1;
  for (int y : f[x])
    if (!vis[y])
      pre(y);
  seq.pb(x);
}
inline void dfs(int x, int t) {
  vis[x] = t;
  for (int y : g[x])
    if (!vis[y])
      dfs(y, t);
}
inline bool check() {
  clr(vis, 0);
  seq.clear();
  for (int i = 1; i <= m; i++)
    if (!vis[i])
      pre(i);
  clr(vis, 0);
  for (int i = m, j = 0; i; i--)
    if (!vis[seq[i - 1]])
      dfs(seq[i - 1], ++j);
  for (int i = 1; i <= cnt; i++)
    if (vis[num[i][0]] == vis[num[i][1]])
      return 0;
  return 1;
}
inline bool check(int D) {
  for (int i = 1; i <= m; i++)
    g[i].clear(), f[i].clear();
  build(1, n * 2, 1);
  for (int i = 1; i <= n; i++) {
    int x = pos(xx[i], i), y = pos(yy[i], i);
    add(num[pp[y]][0], num[pp[x]][1]);
    add(num[pp[x]][0], num[pp[y]][1]);
    get(1, n * 2, pos(xx[i] - D + 1), x - 1, 1, x);
    get(1, n * 2, x + 1, pos(xx[i] + D) - 1, 1, x);
    get(1, n * 2, pos(yy[i] - D + 1), y - 1, 1, y);
    get(1, n * 2, y + 1, pos(yy[i] + D) - 1, 1, y);
  }
  return check();
}

int main() {
#ifdef rqgao2014
  freopen("input.txt", "r", stdin);
#endif
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &xx[i], &yy[i]);
    a[i] = mp(xx[i], i);
    a[i + n] = mp(yy[i], i);
    gmax(inf, xx[i]);
    gmax(inf, yy[i]);
  }
  sort(a + 1, a + n * 2 + 1);
  build(1, n * 2, 1);
  m = cnt * 2;
  for (int i = 1; i <= cnt; i++)
    num[i][0] = i * 2, num[i][1] = i * 2 - 1;
  int l = 0, r = inf;
  while (l < r) {
    int mid = l + r + 1 >> 1;
    if (check(mid))
      l = mid;
    else
      r = mid - 1;
  }
  print(r);
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define sqr(x) ((x) * (x))
#define ll long long
#define ull unsigned long long
#define ui unsigned int
#define ld long double
#define vi vector<int>
#define HEAP(...) priority_queue<__VA_ARGS__>
#define heap(...)                                                              \
  priority_queue<__VA_ARGS__, vector<__VA_ARGS__>, greater<__VA_ARGS__>>
#define pii pair<int, int>
#define pb push_back
#define mp make_pair
#define debuge cerr << "isok" << endl
#define debug(x) cerr << #x << "=" << x << endl
#define dprintf(...) fprintf(stderr, __VA_ARGS__)
#define SS second
#define FF first
#define ls (k << 1)
#define rs (k << 1 | 1)
#define clr(a, x) memset(a, x, sizeof(a))
#define cpy(a, x) memcpy(a, x, sizeof(a))
#define file(x) freopen(x ".in", "r", stdin), freopen(x ".out", "w", stdout)
#define SZ(x) ((int)x.size())
using namespace std;
template <class T> inline void gmin(T &x, const T &y) {
  if (x > y)
    x = y;
}
template <class T> inline void gmax(T &x, const T &y) {
  if (x < y)
    x = y;
}
const int BufferSize = 1 << 16;
char buffer[BufferSize], *Bufferhead, *Buffertail;
bool Terminal;
inline char Getchar() {
  if (Bufferhead == Buffertail) {
    int l = fread(buffer, 1, BufferSize, stdin);
    if (!l) {
      Terminal = 1;
      return 0;
    }
    Buffertail = (Bufferhead = buffer) + l;
  }
  return *Bufferhead++;
}
template <class T> inline bool read(T &x) {
  x = 0;
  char c = Getchar(), rev = 0;
  while (c < '0' || c > '9') {
    c = Getchar();
    rev |= c == '-';
    if (Terminal)
      return 0;
  }
  while (c >= '0' && c <= '9')
    x = x * 10 + c - '0', c = Getchar();
  if (c == '.') {
    c = Getchar();
    double t = 0.1;
    while (c >= '0' && c <= '9')
      x = x + (c - '0') * t, c = Getchar(), t = t / 10;
  }
  x = rev ? -x : x;
  return 1;
}
template <class T1, class T2> inline bool read(T1 &x, T2 &y) {
  return read(x) & read(y);
}
template <class T1, class T2, class T3> inline bool read(T1 &x, T2 &y, T3 &z) {
  return read(x) & read(y) & read(z);
}
template <class T1, class T2, class T3, class T4>
inline bool read(T1 &x, T2 &y, T3 &z, T4 &w) {
  return read(x) & read(y) & read(z) & read(w);
}
inline bool reads(char *x) {
  char c = Getchar();
  while (c < 33 || c > 126) {
    c = Getchar();
    if (Terminal)
      return 0;
  }
  while (c >= 33 && c <= 126)
    (*x++) = c, c = Getchar();
  *x = 0;
  return 1;
}
template <class T> inline void print(T x, const char c = '\n') {
  if (!x) {
    putchar('0');
    putchar(c);
    return;
  }
  if (x < 0)
    putchar('-'), x = -x;
  int m = 0, a[20];
  while (x)
    a[m++] = x % 10, x /= 10;
  while (m--)
    putchar(a[m] + '0');
  putchar(c);
}
//--------------------------------head---------------------------------------------

const int N = 140005, M = 100005, mod = 1e9 + 7;
template <class T, class S> inline void ch(T &x, const S y) {
  x = (x + y) % mod;
}
inline int exp(int x, int y, const int mod = ::mod) {
  int ans = 1;
  while (y) {
    if (y & 1)
      ans = (ll)ans * x % mod;
    x = (ll)x * x % mod;
    y >>= 1;
  }
  return ans;
}

int n, m, inf, cnt, xx[N], yy[N], num[N][2], pp[N];
pii a[N];
int vis[N];
vi g[N], f[N], seq;

inline int pos(int x, int y = 0) {
  return lower_bound(a + 1, a + n * 2 + 1, mp(x, y)) - a;
}
void add(int x, int y) {
  g[x].pb(y);
  f[y].pb(x);
}
inline void build(int l, int r, int k) {
  if (l == r) {
    pp[l] = k;
    gmax(cnt, k);
    return;
  }
  int mid = l + r >> 1;
  build(l, mid, ls);
  build(mid + 1, r, rs);
  add(num[k][0], num[ls][0]);
  add(num[ls][1], num[k][1]);
  add(num[k][0], num[rs][0]);
  add(num[rs][1], num[k][1]);
}
inline void get(int l, int r, int x, int y, int k, int p) {
  if (x > y)
    return;
  if (x <= l && r <= y) {
    add(num[pp[p]][1], num[k][0]);
    add(num[k][1], num[pp[p]][0]);
    return;
  }
  int mid = l + r >> 1;
  if (x <= mid)
    get(l, mid, x, y, ls, p);
  if (y > mid)
    get(mid + 1, r, x, y, rs, p);
}
inline void pre(int x) {
  vis[x] = 1;
  for (int y : f[x])
    if (!vis[y])
      pre(y);
  seq.pb(x);
}
inline void dfs(int x, int t) {
  vis[x] = t;
  for (int y : g[x])
    if (!vis[y])
      dfs(y, t);
}
inline bool check() {
  clr(vis, 0);
  seq.clear();
  for (int i = 1; i <= m; i++)
    if (!vis[i])
      pre(i);
  clr(vis, 0);
  for (int i = m, j = 0; i; i--)
    if (!vis[seq[i - 1]])
      dfs(seq[i - 1], ++j);
  for (int i = 1; i <= cnt; i++)
    if (vis[num[i][0]] == vis[num[i][1]])
      return 0;
  return 1;
}
inline bool check(int D) {
  for (int i = 1; i <= m; i++)
    g[i].clear(), f[i].clear();
  build(1, n * 2, 1);
  for (int i = 1; i <= n; i++) {
    int x = pos(xx[i], i), y = pos(yy[i], i);
    add(num[pp[y]][0], num[pp[x]][1]);
    add(num[pp[x]][0], num[pp[y]][1]);
    get(1, n * 2, pos(xx[i] - D + 1), x - 1, 1, x);
    get(1, n * 2, x + 1, pos(xx[i] + D) - 1, 1, x);
    get(1, n * 2, pos(yy[i] - D + 1), y - 1, 1, y);
    get(1, n * 2, y + 1, pos(yy[i] + D) - 1, 1, y);
  }
  return check();
}

int main() {
#ifdef rqgao2014
  freopen("input.txt", "r", stdin);
#endif
  scanf("%d", &n);
  for (int i = 1; i <= n; i++) {
    scanf("%d%d", &xx[i], &yy[i]);
    a[i] = mp(xx[i], i);
    a[i + n] = mp(yy[i], i);
    gmax(inf, xx[i]);
    gmax(inf, yy[i]);
  }
  sort(a + 1, a + n * 2 + 1);
  build(1, n * 2, 1);
  m = cnt * 2;
  for (int i = 1; i <= cnt; i++)
    num[i][0] = i * 2, num[i][1] = i * 2 - 1;
  int l = 0, r = inf;
  while (l < r) {
    int mid = l + r + 1 >> 1;
    if (check(mid))
      l = mid;
    else
      r = mid - 1;
  }
  print(r);
  return 0;
}