Problem p02678 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define all(a) a.begin(), a.end()
#define pb push_back
#define mp make_pair
typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<ll, int> pli;
typedef pair<int, int> pii;
#define rep(i, a, b) for (ll i = a; i < b; i++)
#define qrep(que, ite) for (auto ite = begin(que); ite != end(que); ite++)
const int max_n = 1e5;
const ll mod = 1e9 + 7;
const ll INF = 1e17;
const int inf = 1e5;
typedef long double ld;
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;
}
ll gcd(ll a, ll b) { return a ? gcd(b % a, a) : b; }
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};

int main() {
  int N, M;
  cin >> N >> M;
  vector<vector<int>> v(100000);
  vector<int> ans(N, -1);
  rep(i, 0, M) {
    int x, y;
    cin >> x >> y;
    --x;
    --y;
    v[x].pb(y);
    v[y].pb(x);
  }
  if (v[0].size() == 0) {
    cout << "No" << endl;
    return 0;
  }
  queue<int> que;
  que.push(0);
  while (que.size()) {
    int now = que.front();
    que.pop();

    for (auto j : v[now]) {
      if (ans[j] >= 0)
        continue;
      ans[j] = now;
      que.push(j);
    }
  }
  cout << "Yes" << endl;
  for (int i = 1; i < N; i++) {
    cout << ans[i] + 1 << endl;
  }
  return 0;
}


Error: WA

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#define fi first
#define se second
#define all(a) a.begin(), a.end()
#define pb push_back
#define mp make_pair
typedef long long ll;
typedef pair<ll, ll> P;
typedef pair<ll, int> pli;
typedef pair<int, int> pii;
#define rep(i, a, b) for (ll i = a; i < b; i++)
#define qrep(que, ite) for (auto ite = begin(que); ite != end(que); ite++)
const int max_n = 1e5;
const ll mod = 1e9 + 7;
const ll INF = 1e17;
const int inf = 1e5;
typedef long double ld;
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;
}
ll gcd(ll a, ll b) { return a ? gcd(b % a, a) : b; }
int dx[4] = {0, 0, 1, -1};
int dy[4] = {1, -1, 0, 0};
ll mo = 998244353;
struct UnionFind {
  vector<int> par;

  UnionFind(int n) : par(n, -1) {}
  void init(int n) { par.assign(n, -1); }

  int root(int x) {
    if (par[x] < 0)
      return x;
    else
      return par[x] = root(par[x]);
  }

  bool issame(int x, int y) { return root(x) == root(y); }

  bool merge(int x, int y) {
    x = root(x);
    y = root(y);
    if (x == y)
      return false;
    if (par[x] > par[y])
      swap(x, y); // merge technique
    par[x] += par[y];
    par[y] = x;
    return true;
  }

  int size(int x) { return -par[root(x)]; }
};
struct SegmentTree {
  int N;
  vector<int> node;

public:
  void intit(vector<int> v) {
    int sz = v.size();
    N = 1;
    while (N < sz)
      N *= 2;
    node.resize(N);
    for (int i = 0; i < sz; i++)
      node[i + N - 1] = v[i];
    for (int i = N - 2; i >= 0; i--)
      node[i] = min(node[i * 2 + 1], node[i * 2 + 2]);
  }
  void update(int x, int val) {
    x += N - 1;
    node[x + N - 1] = val;
    while (x > 0) {
      x = (x - 1) / 2;
      node[x] = min(node[x * 2 + 1], node[x * 2 + 2]);
    }
  }
  int getmin(int a, int b, int k, int l, int r) {
    if (b <= l || r <= a)
      return inf;
    else if (a <= l && r <= b)
      return node[k];
    else {
      int vl = getmin(a, b, 2 * k + 1, l, (l + r) / 2);
      int vr = getmin(a, b, 2 * k + 2, (l + r) / 2, r);
      return min(vl, vr);
    }
  }
};
vector<vector<int>> v;
vector<int> ans;
void dfs(int now, int pre) {
  if (ans[now] >= 0)
    return;
  ans[now] = pre;
  for (auto j : v[now]) {
    if (j == pre)
      continue;
    dfs(j, now);
  }
}
int main() {
  int N, M;
  cin >> N >> M;
  v.resize(M);
  ans.resize(N, -1);
  rep(i, 0, M) {
    int x, y;
    cin >> x >> y;
    --x;
    --y;
    v[x].pb(y);
    v[y].pb(x);
  }
  if (v[0].size() == 0) {
    cout << "No" << endl;
    return 0;
  }
  queue<int> que;
  que.push(0);
  while (que.size()) {
    int now = que.front();
    que.pop();

    for (auto j : v[now]) {
      if (ans[j] >= 0)
        continue;
      ans[j] = now;
      que.push(j);
    }
  }
  rep(i, 1, N) { cout << ans[i] + 1 << endl; }
  return 0;
}