Problem p02678 (C++)

Buggy submission (status: Time Limit Exceeded):
// include
// ------------------------------------------------
#include <algorithm>
#include <bits/stdc++.h>
#include <math.h>

using namespace std;

// func
// ------------------------------------------------
int CalcSumOfDigit(int n); // 各桁の和を計算する。
int getDigit(int n);       // 数字の桁数を取得する。
string upper(string str);  // 英字を大文字に変換する。
string lower(string str);  // 英字を小文字に変換する。

// class
// ------------------------------------------------
class Combi {
public:
  Combi();
  long long Combination(long long n, long long k);

private:
  vector<vector<long long>> memo;
  long long n_num;
  long long k_num;
  void Resize(long long n, long long k);
};

// define
// ------------------------------------------------
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define sz(a) int((a).size())
#define rep(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define repe(i, n) for (int(i) = 0; (i) <= (n); (i)++)
#define vsort(v) sort((v).begin(), (v).end())
#define rvsort(v) sort(rall((v)))
#define vi vector<int>
#define GCD(a, b) __gcd((a), (b))
#define LCM(a, b) (a) / GCD((a), (b)) * (b)
#define kiriage(a, b) ((a) + (b)-1) / (b)

const int INF = 1e9;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<long> vll;
// code
// ------------------------------------------------
int main() {

  ll n, m;
  cin >> n >> m;

  vector<vector<ll>> Graph(n);
  vll a(n, -1);

  rep(i, m) {
    ll a, b;
    cin >> a >> b;
    a--;
    b--;
    Graph[a].push_back(b);
    Graph[b].push_back(a);
  }

  queue<ll> q;

  ll now = 0;
  ll before = 0;
  vll seen(n);
  q.push(now);

  while (!q.empty()) {
    now = q.front();
    q.pop();

    seen[now] = 1;

    for (auto itr = Graph[now].begin(); itr != Graph[now].end(); ++itr) {
      ll next = *itr;
      if (a[next] == -1) {
        a[next] = now;
      }
      if (seen[next] != 1) {
        q.push(next);
      }
    }
    before = now;
  }

  bool ans = true;
  for (ll i = 1; i < n; ++i) {
    if (a[i] == -1) {
      ans = false;
      break;
    }
  }

  if (ans)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
  for (ll i = 1; i < n; ++i) {
    cout << a[i] + 1 << endl;
  }

  return 0;
}
// funcの実体
// ------------------------------------------------
int getDigit(int n) {
  int i = 1;
  while (1) {
    n = n / 10;
    if (n == 1)
      break;
    i++;
  }
  return i;
}
int CalcSumOfDigit(int n) {
  int s = 0;
  while (n) {
    s += n % 10;
    n = n / 10;
  }
  return s;
}

string upper(string str) {
  for (auto itr = str.begin(); itr != str.end(); itr++) {
    if (97 <= *itr && *itr <= 122) {
      *itr = *itr - 32;
    }
  }
  return str;
}

string lower(string str) {
  for (auto itr = str.begin(); itr != str.end(); itr++) {
    if (65 <= *itr && *itr <= 90) {
      *itr = *itr + 32;
    }
  }
  return str;
}

Combi::Combi() {
  n_num = -1;
  k_num = -1;
};
ll Combi::Combination(ll n, ll k) {
  Resize(n, k);

  ll ret;
  if (memo[n][k] != 0) {
    ret = memo[n][k];
  } else if (n == k || k == 0) {
    memo[n][k] = 1;
    ret = 1;
  } else {
    ret = Combination(n - 1, k - 1) + Combination(n - 1, k);
    memo[n][k] = ret;
  }
  return ret;
}

void Combi::Resize(ll n, ll k) {
  if (n_num <= n || k_num <= k) {
    n_num = (n + 1) * 2;
    k_num = (k + 1) * 2;
    memo.resize(n_num);
    for (auto itr = memo.begin(); itr != memo.end(); ++itr) {
      itr->resize(k_num);
    }
  }
}

Fixed submission:
// include
// ------------------------------------------------
#include <algorithm>
#include <bits/stdc++.h>
#include <math.h>

using namespace std;

// func
// ------------------------------------------------
int CalcSumOfDigit(int n); // 各桁の和を計算する。
int getDigit(int n);       // 数字の桁数を取得する。
string upper(string str);  // 英字を大文字に変換する。
string lower(string str);  // 英字を小文字に変換する。

// class
// ------------------------------------------------
class Combi {
public:
  Combi();
  long long Combination(long long n, long long k);

private:
  vector<vector<long long>> memo;
  long long n_num;
  long long k_num;
  void Resize(long long n, long long k);
};

// define
// ------------------------------------------------
#define all(a) (a).begin(), (a).end()
#define rall(a) (a).rbegin(), (a).rend()
#define sz(a) int((a).size())
#define rep(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define repe(i, n) for (int(i) = 0; (i) <= (n); (i)++)
#define vsort(v) sort((v).begin(), (v).end())
#define rvsort(v) sort(rall((v)))
#define vi vector<int>
#define GCD(a, b) __gcd((a), (b))
#define LCM(a, b) (a) / GCD((a), (b)) * (b)
#define kiriage(a, b) ((a) + (b)-1) / (b)

const int INF = 1e9;

typedef long long ll;
typedef unsigned long long ull;
typedef vector<long> vll;
// code
// ------------------------------------------------
int main() {

  ll n, m;
  cin >> n >> m;

  vector<vector<ll>> Graph(n);
  vll a(n, -1);

  rep(i, m) {
    ll a, b;
    cin >> a >> b;
    a--;
    b--;
    Graph[a].push_back(b);
    Graph[b].push_back(a);
  }

  queue<ll> q;

  ll now = 0;
  ll before = 0;
  vll seen(n);
  q.push(now);

  while (!q.empty()) {
    now = q.front();
    q.pop();

    if (seen[now] == 1) {
      continue;
    }

    seen[now] = 1;

    for (auto itr = Graph[now].begin(); itr != Graph[now].end(); ++itr) {
      ll next = *itr;
      if (a[next] == -1) {
        a[next] = now;
      }
      if (seen[next] != 1) {
        q.push(next);
      }
    }
    before = now;
  }

  bool ans = true;
  for (ll i = 1; i < n; ++i) {
    if (a[i] == -1) {
      ans = false;
      break;
    }
  }

  if (ans)
    cout << "Yes" << endl;
  else
    cout << "No" << endl;
  for (ll i = 1; i < n; ++i) {
    cout << a[i] + 1 << endl;
  }

  return 0;
}
// funcの実体
// ------------------------------------------------
int getDigit(int n) {
  int i = 1;
  while (1) {
    n = n / 10;
    if (n == 1)
      break;
    i++;
  }
  return i;
}
int CalcSumOfDigit(int n) {
  int s = 0;
  while (n) {
    s += n % 10;
    n = n / 10;
  }
  return s;
}

string upper(string str) {
  for (auto itr = str.begin(); itr != str.end(); itr++) {
    if (97 <= *itr && *itr <= 122) {
      *itr = *itr - 32;
    }
  }
  return str;
}

string lower(string str) {
  for (auto itr = str.begin(); itr != str.end(); itr++) {
    if (65 <= *itr && *itr <= 90) {
      *itr = *itr + 32;
    }
  }
  return str;
}

Combi::Combi() {
  n_num = -1;
  k_num = -1;
};
ll Combi::Combination(ll n, ll k) {
  Resize(n, k);

  ll ret;
  if (memo[n][k] != 0) {
    ret = memo[n][k];
  } else if (n == k || k == 0) {
    memo[n][k] = 1;
    ret = 1;
  } else {
    ret = Combination(n - 1, k - 1) + Combination(n - 1, k);
    memo[n][k] = ret;
  }
  return ret;
}

void Combi::Resize(ll n, ll k) {
  if (n_num <= n || k_num <= k) {
    n_num = (n + 1) * 2;
    k_num = (k + 1) * 2;
    memo.resize(n_num);
    for (auto itr = memo.begin(); itr != memo.end(); ++itr) {
      itr->resize(k_num);
    }
  }
}