Problem p02347 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <cstdio>
#include <vector>
using namespace std;

class Node {
public:
  int location;
  int p, l, r;

  Node() {}
};

class Point {
public:
  int id, x, y;

  Point() {}
  Point(int id, int x, int y) : id(id), x(x), y(y) {}

  bool operator<(const Point &p) const { return id < p.id; }

  void print() { printf("%d\\n", id); }
};

const int MAX_N = 500000;
const int NIL = -1;

int n;
Point P[MAX_N];
Node T[MAX_N];
int np;

bool lessX(const Point &p1, const Point &p2) { return p1.x < p2.x; }
bool lessY(const Point &p1, const Point &p2) { return p1.y < p2.y; }

int makeKDTree(int l, int r, int d) {
  if (!(l < r))
    return NIL;

  int mid = (l + r) / 2;
  int t = np++;
  if (d % 2 == 0) {
    sort(P + l, P + r, lessX);
  } else {
    sort(P + l, P + r, lessY);
  }

  T[t].location = mid;
  T[t].l = makeKDTree(l, mid, d + 1);
  T[t].r = makeKDTree(mid + 1, r, d + 1);

  return t;
}

void find(int v, int sx, int tx, int sy, int ty, int d, vector<Point> &ans) {
  int x = P[T[v].location].x;
  int y = P[T[v].location].y;

  if (sx <= x && x <= tx && sy <= y && y <= ty) {
    ans.push_back(P[T[v].location]);
  }

  if (d % 2 == 0) {
    if (T[v].l != NIL) {
      if (sx <= x)
        find(T[v].l, sx, tx, sy, ty, d + 1, ans);
    }
    if (T[v].r != NIL) {
      if (x <= tx)
        find(T[v].r, sx, tx, sy, ty, d + 1, ans);
    }
  } else {
    if (T[v].l != NIL) {
      if (sy <= y)
        find(T[v].l, sx, tx, sy, ty, d + 1, ans);
    }
    if (T[v].r != NIL) {
      if (y <= ty)
        find(T[v].r, sx, tx, sy, ty, d + 1, ans);
    }
  }
}

int main(void) {
  int x, y;
  scanf("%d", &n);
  for (int i = 0; i < n; i++) {
    scanf("%d %d", &x, &y);
    P[i] = Point(i, x, y);
    T[i].l = T[i].r = T[i].p = NIL;
  }

  np = 0;
  int root = makeKDTree(0, n, 0);

  int q;
  scanf("%d", &q);
  int sx, tx, sy, ty;
  for (int i = 0; i < q; i++) {
    vector<Point> ans;
    scanf("%d %d %d %d", &sx, &tx, &sy, &ty);
    find(root, sx, tx, sy, ty, 0, ans);
    sort(ans.begin(), ans.end());
    for (auto j = 0; j < ans.size(); j++)
      ans[j].print();
    putchar('\\n');
  }

  return 0;
}

Error: WA

Fixed submission:

#include <iostream>
#include <vector>
using namespace std;

class DisjointSet {
public:
  vector<int> rank, p;

  DisjointSet(){};
  DisjointSet(int s) {
    rank.resize(s, 0);
    p.resize(s, 0);
    for (int i = 0; i < s; i++)
      makeSet(i);
  }

  void makeSet(int x) {
    p[x] = x;
    rank[x] = 0;
  }

  bool same(int x, int y) { return findSet(x) == findSet(y); }

  void unite(int x, int y) { link(findSet(x), findSet(y)); }

  void link(int x, int y) {
    if (rank[x] > rank[y]) {
      p[y] = x;
    } else {
      p[x] = y;
      if (rank[x] == rank[y]) {
        rank[y]++;
      }
    }
  }

  int findSet(int x) {
    while (x != p[x]) {
      x = p[x];
    }
    return x;
  }
};

int main(void) {
  int n, q;
  cin >> n >> q;
  DisjointSet ds = DisjointSet(n);

  for (int i = 0; i < q; i++) {
    int com, x, y;
    cin >> com >> x >> y;
    if (com == 0) {
      ds.unite(x, y);
    } else {
      if (ds.same(x, y)) {
        cout << 1 << endl;
      } else {
        cout << 0 << endl;
      }
    }
  }

  return 0;
}