Problem p02630 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for (int i = 1; i <= (int)(n); i++)
#define drep(i, n) for (int i = (n)-1; i >= 0; i--)
#define ALL(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;

// Mod int
const int mod = 1000000007;
// const int mod = 998244353;
struct mint {
  ll x;
  mint() : x(0) {}
  mint(ll x) : x((x % mod + mod) % mod) {}
  // mint(ll x):x(x){}
  mint &fix() {
    x = (x % mod + mod) % mod;
    return *this;
  }
  mint operator-() const { return mint(0) - *this; }
  mint &operator+=(const mint &a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint &a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint &a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint &a) const { return mint(*this) += a; }
  mint operator-(const mint &a) const { return mint(*this) -= a; }
  mint operator*(const mint &a) const { return mint(*this) *= a; }
  bool operator<(const mint &a) const { return x < a.x; }
  bool operator==(const mint &a) const { return x == a.x; }
};
istream &operator>>(istream &i, mint &a) {
  i >> a.x;
  return i;
}
ostream &operator<<(ostream &o, const mint &a) {
  o << a.x;
  return o;
}
//

int main() {
  int n;
  cin >> n;
  vi a(100005);
  ll sum = 0;
  rep(i, n) {
    int A;
    cin >> A;
    a[A]++;
    sum += ll(A);
  }
  int q;
  cin >> q;
  vi b(q), c(q);
  rep(i, q) cin >> b[i] >> c[i];
  rep(i, q) {
    ll sa = ll(c[i] - b[i]);
    sum += ll(sa * a[b[i]]);
    a[c[i]] += a[b[i]];
    a[b[i]] = 0;
    cout << sum << endl;
  }
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
#define rep(i, n) for (int i = 0; i < (int)(n); i++)
#define rrep(i, n) for (int i = 1; i <= (int)(n); i++)
#define drep(i, n) for (int i = (n)-1; i >= 0; i--)
#define ALL(x) (x).begin(), (x).end()
using namespace std;
typedef long long ll;
typedef pair<int, int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
const ll LINF = 1001002003004005006ll;
const int INF = 1001001001;

// Mod int
const int mod = 1000000007;
// const int mod = 998244353;
struct mint {
  ll x;
  mint() : x(0) {}
  mint(ll x) : x((x % mod + mod) % mod) {}
  // mint(ll x):x(x){}
  mint &fix() {
    x = (x % mod + mod) % mod;
    return *this;
  }
  mint operator-() const { return mint(0) - *this; }
  mint &operator+=(const mint &a) {
    if ((x += a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator-=(const mint &a) {
    if ((x += mod - a.x) >= mod)
      x -= mod;
    return *this;
  }
  mint &operator*=(const mint &a) {
    (x *= a.x) %= mod;
    return *this;
  }
  mint operator+(const mint &a) const { return mint(*this) += a; }
  mint operator-(const mint &a) const { return mint(*this) -= a; }
  mint operator*(const mint &a) const { return mint(*this) *= a; }
  bool operator<(const mint &a) const { return x < a.x; }
  bool operator==(const mint &a) const { return x == a.x; }
};
istream &operator>>(istream &i, mint &a) {
  i >> a.x;
  return i;
}
ostream &operator<<(ostream &o, const mint &a) {
  o << a.x;
  return o;
}
//

int main() {
  int n;
  cin >> n;
  vi a(n + 1);
  ll sum = 0;
  rep(i, n) {
    int A;
    cin >> A;
    a[A]++;
    sum += ll(A);
  }
  int q;
  cin >> q;
  vi b(q), c(q);
  rep(i, q) cin >> b[i] >> c[i];
  rep(i, q) {
    ll sa = ll(c[i] - b[i]);
    // cout << b[i] << " " << c[i] << " " << sa << " ";
    sum += sa * a[b[i]];
    a[c[i]] += a[b[i]];
    cout << sum << endl;
  }
}