Problem p02573 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define ll long long //
#define rp(i, a, b) for (ll i = a; i < b; i++)
#define r(i, n) for (ll i = 0; i < n; i++)
#define rt return
#define db double
#define ldb long double
#define vd void
#define p(x) cout << (x) << endl;
#define psc(x) cout << setprecision(50) << (x) << endl;
#define precise(x) cout << setprecision(50) << x << endl;
#define ce continue;
#define bl bool
#define r0 rt 0;
#define r1 rt 1;
#define elif else if
#define bk break;
#define A p("A")
#define B p("B")
#define C p("C")
#define D p("D")
#define E p("E")
#define F p("F")
#define S(a) sort(a.begin(), a.end());
#define R(a) reverse(a.begin(), a.end());
#define cl cout << endl;
#define pb(x) push_back(x);
#define str string
using namespace std;
void Cond(int g) {
  if (g)
    p("YES") else p("NO") rt;
}
void cond(int g) {
  if (g)
    p("Yes") else p("No") rt;
}
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (a % b == 0)
    rt b;
  gcd(b, a % b);
}
str su = "0123456789";
str m1 = "abcdefghijklmnopqrstuvwxyz";
str m2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
map<char, ll> m5;
typedef pair<ll, ll> P;
const ll INF = (ll)1e18 + 10;
ll t1 = 0, t2 = 0, t3 = 0, t4 = 0, t5 = 0, t6 = 0, t7 = 0, t8 = 0, g = 0,
   ans = 0;
ll n = 0, m = 0, mx = -INF, mn = INF, ct = 0, cnt = 0;
ll sum = 0, mask = 0;

ll k;
set<P> pst;
set<ll> st;
ll powmod(ll a, ll b, ll x) { //(a^b)modx
  if (!b)
    r1 if (!(b % 2)) { // B
      ll t = powmod(a, b / 2, x);
      rt t *t % x;
    }
  rt((a)*powmod(a, b - 1, x)) % x;
}
void di() {
  m5['a'] = 0;
  m5['b'] = 1;
  m5['c'] = 2;
  m5['d'] = 3;
  m5['e'] = 4;
  m5['f'] = 5;
  m5['g'] = 6;
  m5['h'] = 7;
  m5['i'] = 8;
  m5['j'] = 9;
  m5['k'] = 10;
  m5['l'] = 11;
  m5['m'] = 12;
  m5['n'] = 13;
  m5['o'] = 14;
  m5['p'] = 15;
  m5['q'] = 16;
  m5['r'] = 17;
  m5['s'] = 18;
  m5['t'] = 19;
  m5['u'] = 20;
  m5['v'] = 21;
  m5['w'] = 22;
  m5['x'] = 23;
  m5['y'] = 24;
  m5['z'] = 25;
}
map<ll, ll> mp;
typedef std::vector<ll> vl;
typedef pair<ll, ll> P;
typedef pair<ll, P> P2;
typedef struct edge2 {
  P tos;
  ll cost;
} EDGE2;
typedef struct edge1 {
  ll to, cost;
} EDGE;
bl used[(ll)1e6];
const ll M = (ll)1e9 + 7;
ll fac[1000007], finv[1000007], inv[1000007];
void initcmb() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < 1000007; i++) {
    fac[i] = fac[i - 1] * i % M;
    inv[i] = M - inv[M % i] * (M / i) % M;
    finv[i] = finv[i - 1] * inv[i] % M;
  }
}
ll cmb(ll n, ll k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % M) % M;
}
db pi =
    3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651328230664709384460955058223172535940812848111745028410270193852110555964462294895493038196;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const ll MAX = (ll)1e5 * 3;
vl rui(MAX);
vl ru1(MAX);
vl ru2(MAX);

vector<vector<EDGE>> G(1e6);

// int -2,147,483,648 ～ 2,147,483,647
// alt f3

vector<vector<ll>> a(1e6);

vl color(1e5, -1);

vd dfs(ll vtx) {
  color[vtx] = k;
  used[vtx] = true;
  r(i, a[vtx].size()) {

    if (used[a[vtx][i]] == false) {
      dfs(a[vtx][i]);
    }
  }
  rt;
}
int main() { // swap(ary１,ary２)
  // a.erase(a.begin()+5),a.insert(a.begin()+3,tmp)
  // ios_base::sync_with_stdio(0); cin.tie(0);
  //  long long 型でREになる時はint型で書き直す
  clock_t start = clock(); // timecalc

  k = 1;
  cin >> n >> m;
  set<P> pst;
  r(i, m) {
    cin >> t1 >> t2;
    mn = min(t1, t2);
    mx = (t1, t2);
    pst.insert({t1, t2});
    st.insert(t1);
    st.insert(t2);
  }
  for (P i : pst) {
    t1 = i.first;
    t2 = i.second;
    a[t1].pb(t2);
    a[t2].pb(t1);
  }

  rp(i, 1, n + 1) {
    if (used[i] == false) {
      dfs(i);
    }
    k++;
  }
  //  p("COLORS")
  //  rp(i, 1, n + 1) {

  //      p(color[i])
  //  }
  // // p("END ")
  k--; // sup val .
  rp(i, 1, n + 1) { mp[color[i]]++; }
  mx = -INF;
  rp(i, 1, k + 1) {
    //      cout << i << " th cols num " << mp[i] << endl;
    chmax(mx, mp[i]);
  }
  p(mx)

      clock_t end = clock(); //
  const double time =
      static_cast<double>(end - start) / CLOCKS_PER_SEC * 1000.0; // timecalc
  // printfz("time %lf[ms]\n", time);//
  return 0;
} // main


Fixed submission:
#include <bits/stdc++.h>
#define ll long long //
#define rp(i, a, b) for (ll i = a; i < b; i++)
#define r(i, n) for (ll i = 0; i < n; i++)
#define rt return
#define db double
#define ldb long double
#define vd void
#define p(x) cout << (x) << endl;
#define psc(x) cout << setprecision(50) << (x) << endl;
#define precise(x) cout << setprecision(50) << x << endl;
#define ce continue;
#define bl bool
#define r0 rt 0;
#define r1 rt 1;
#define elif else if
#define bk break;
#define A p("A")
#define B p("B")
#define C p("C")
#define D p("D")
#define E p("E")
#define F p("F")
#define S(a) sort(a.begin(), a.end());
#define R(a) reverse(a.begin(), a.end());
#define cl cout << endl;
#define pb(x) push_back(x);
#define str string
using namespace std;
void Cond(int g) {
  if (g)
    p("YES") else p("NO") rt;
}
void cond(int g) {
  if (g)
    p("Yes") else p("No") rt;
}
ll gcd(ll a, ll b) {
  if (a < b)
    swap(a, b);
  if (a % b == 0)
    rt b;
  gcd(b, a % b);
}
str su = "0123456789";
str m1 = "abcdefghijklmnopqrstuvwxyz";
str m2 = "ABCDEFGHIJKLMNOPQRSTUVWXYZ";
map<char, ll> m5;
typedef pair<ll, ll> P;
const ll INF = (ll)1e18 + 10;
ll t1 = 0, t2 = 0, t3 = 0, t4 = 0, t5 = 0, t6 = 0, t7 = 0, t8 = 0, g = 0,
   ans = 0;
ll n = 0, m = 0, mx = -INF, mn = INF, ct = 0, cnt = 0;
ll sum = 0, mask = 0;

ll k;
set<P> pst;
set<ll> st;
ll powmod(ll a, ll b, ll x) { //(a^b)modx
  if (!b)
    r1 if (!(b % 2)) { // B
      ll t = powmod(a, b / 2, x);
      rt t *t % x;
    }
  rt((a)*powmod(a, b - 1, x)) % x;
}
void di() {
  m5['a'] = 0;
  m5['b'] = 1;
  m5['c'] = 2;
  m5['d'] = 3;
  m5['e'] = 4;
  m5['f'] = 5;
  m5['g'] = 6;
  m5['h'] = 7;
  m5['i'] = 8;
  m5['j'] = 9;
  m5['k'] = 10;
  m5['l'] = 11;
  m5['m'] = 12;
  m5['n'] = 13;
  m5['o'] = 14;
  m5['p'] = 15;
  m5['q'] = 16;
  m5['r'] = 17;
  m5['s'] = 18;
  m5['t'] = 19;
  m5['u'] = 20;
  m5['v'] = 21;
  m5['w'] = 22;
  m5['x'] = 23;
  m5['y'] = 24;
  m5['z'] = 25;
}
map<ll, ll> mp;
typedef std::vector<ll> vl;
typedef pair<ll, ll> P;
typedef pair<ll, P> P2;
typedef struct edge2 {
  P tos;
  ll cost;
} EDGE2;
typedef struct edge1 {
  ll to, cost;
} EDGE;
bl used[(ll)1e6];
const ll M = (ll)1e9 + 7;
ll fac[1000007], finv[1000007], inv[1000007];
void initcmb() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < 1000007; i++) {
    fac[i] = fac[i - 1] * i % M;
    inv[i] = M - inv[M % i] * (M / i) % M;
    finv[i] = finv[i - 1] * inv[i] % M;
  }
}
ll cmb(ll n, ll k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % M) % M;
}
db pi =
    3.14159265358979323846264338327950288419716939937510582097494459230781640628620899862803482534211706798214808651328230664709384460955058223172535940812848111745028410270193852110555964462294895493038196;

template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return 1;
  }
  return 0;
}
const ll MAX = (ll)1e5 * 3;
vl rui(MAX);
vl ru1(MAX);
vl ru2(MAX);

vector<vector<EDGE>> G(1e6);

// int -2,147,483,648 ～ 2,147,483,647
// alt f3

vector<vector<ll>> a(1e5 * 3);

vl color(1e5 * 3, -1);

vd dfs(ll vtx) {
  color[vtx] = k;
  used[vtx] = true;
  r(i, a[vtx].size()) {

    if (used[a[vtx][i]] == false) {
      dfs(a[vtx][i]);
    }
  }
  rt;
}
int main() { // swap(ary１,ary２)
  // a.erase(a.begin()+5),a.insert(a.begin()+3,tmp)
  // ios_base::sync_with_stdio(0); cin.tie(0);
  //  long long 型でREになる時はint型で書き直す
  clock_t start = clock(); // timecalc

  k = 1;
  cin >> n >> m;
  set<P> pst;
  r(i, m) {
    cin >> t1 >> t2;
    mn = min(t1, t2);
    mx = (t1, t2);
    pst.insert({t1, t2});
    st.insert(t1);
    st.insert(t2);
  }
  for (P i : pst) {
    t1 = i.first;
    t2 = i.second;
    a[t1].pb(t2);
    a[t2].pb(t1);
  }

  rp(i, 1, n + 1) {
    if (used[i] == false) {
      dfs(i);
    }
    k++;
  }
  //  p("COLORS")
  //  rp(i, 1, n + 1) {

  //      p(color[i])
  //  }
  // // p("END ")
  k--; // sup val .
  rp(i, 1, n + 1) { mp[color[i]]++; }
  mx = -INF;
  rp(i, 1, k + 1) {
    //      cout << i << " th cols num " << mp[i] << endl;
    chmax(mx, mp[i]);
  }
  p(mx)

      clock_t end = clock(); //
  const double time =
      static_cast<double>(end - start) / CLOCKS_PER_SEC * 1000.0; // timecalc
  // printfz("time %lf[ms]\n", time);//
  return 0;
} // main