Problem p00441 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
template <class T> inline T sqr(T x) { return x * x; }

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i, c)                                                             \\
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define exist(s, e) ((s).find(e) != (s).end())
#define range(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) range(i, 0, n)
#define clr(a, b) memset((a), (b), sizeof(a))
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \\
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi = acos(-1.0);
const ll INF = 1LL << 62;
const int inf = 1 << 29;

int x[3010];
int y[3010];
bool board[5010][5010];

int main(void) {
  int n;
  while (cin >> n, n) {

    rep(i, 5010) rep(j, 5010) board[i][j] = false;
    rep(i, n) {
      cin >> x[i] >> y[i];
      board[x[i]][y[i]] = true;
    }
    int cmax = 0;
    rep(i, n) rep(j, n) {
      int dx = x[j] - x[i];
      int dy = y[j] - y[i];

      int x3 = x[i] - dy;
      int y3 = y[i] + dx;

      int x4 = x[j] - dy;
      int y4 = y[j] + dx;

      if (x3 < 0 || 5000 < x3 || y3 < 0 || 5000 < y3 || x4 < 0 || 5000 < x4 ||
          y4 < 0 || 5000 < y4)
        continue;

      if (board[x3][y3] && board[x4][y4])
        cmax = max(cmax, dx * dx + dy * dy);
    }
    cout << cmax << endl;
  }
  return 0;
}

Error: 0

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <deque>
#include <functional>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>

using namespace std;

inline int toInt(string s) {
  int v;
  istringstream sin(s);
  sin >> v;
  return v;
}
template <class T> inline string toString(T x) {
  ostringstream sout;
  sout << x;
  return sout.str();
}
template <class T> inline T sqr(T x) { return x * x; }

typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<string> vs;
typedef pair<int, int> pii;
typedef long long ll;

#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define pb push_back
#define mp make_pair
#define each(i, c)                                                             \\
  for (typeof((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define exist(s, e) ((s).find(e) != (s).end())
#define range(i, a, b) for (int i = (a); i < (b); ++i)
#define rep(i, n) range(i, 0, n)
#define clr(a, b) memset((a), (b), sizeof(a))
#define dump(x) cerr << #x << " = " << (x) << endl;
#define debug(x)                                                               \\
  cerr << #x << " = " << (x) << " (L" << __LINE__ << ")"                       \\
       << " " << __FILE__ << endl;

const double eps = 1e-10;
const double pi = acos(-1.0);
const ll INF = 1LL << 62;
const int inf = 1 << 29;

int x[3010];
int y[3010];
bool board[5010][5010];

int main(void) {
  int n;
  while (cin >> n, n) {

    rep(i, 5010) rep(j, 5010) board[i][j] = false;
    rep(i, n) {
      cin >> x[i] >> y[i];
      board[x[i]][y[i]] = true;
    }
    int cmax = 0;
    rep(i, n) rep(j, n) {
      int dx = x[j] - x[i];
      int dy = y[j] - y[i];
      if (board[x[i] - dy][y[i] + dx] && board[x[j] - dy][y[j] + dx])
        cmax = max(cmax, dx * dx + dy * dy);
    }
    cout << cmax << endl;
  }
  return 0;
}

//  p1(x1,y1) p2(x2,y2) p2(