Problem p03690 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
// #include "stdafx.h"
// #pragma warning(disable : 4996) //_CRT_SECURE_NO_WARNINGS
using namespace std;
#define gc getchar_unlocked
#define fo(i, n) for (i = 0; i < n; i++)
#define Fo(i, k, n) for (i = k; k < n ? i < n : i > n; k < n ? i += 1 : i -= 1)
#define ll long long
#define si(x) scanf("%d", &x)
#define sl(x) scanf("%lld", &x)
#define ss(s) scanf("%s", s)
#define pi(x) printf("%d\n", x)
#define pl(x) printf("%lld\n", x)
#define ps(s) printf("%s\n", s)
#define deb(x) cout << #x << "=" << x << endl
#define deb2(x, y) cout << #x << "=" << x << "," << #y << "=" << y << endl
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof(x))
#define sortall(x) sort(all(x))
#define tr(it, a) for (auto it = a.begin(); it != a.end(); it++)
#define PI 3.1415926535897932384626
typedef pair<int, int> pii;
typedef pair<ll, ll> pl;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pii> vpii;
typedef vector<pl> vpl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
int mpow(int base, int exp);
void ipgraph(int m);
int dfs(int u);
const int mod = 1000000007;
const int N = 3e5, M = N;
//=======================

vi g[N];
int a[N];
int b[N];
map<int, int> vis;

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int i, n, k, j;
  cin >> n;
  int x = 0;
  multiset<int> A;
  fo(i, n) cin >> a[i + 1], x ^= a[i + 1], A.insert(a[i + 1]);
  a[0] = x;
  A.insert(x);
  fo(i, n) {
    cin >> b[i + 1];
    if (A.find(b[i + 1]) == A.end()) {
      cout << -1 << endl;
      return 0;
    }
    A.erase(A.find(b[i + 1]));
  }
  b[0] = *A.begin();
  fo(i, n + 1) { g[b[i]].pb(a[i]); }
  int ans = max(1, dfs(a[0])) - 1;
  if (a[0] == b[0] and ans)
    ans++;
  Fo(i, 1, n + 1) {
    if (!vis[a[i]]) {
      x = dfs(a[i]);
      if (x)
        ans += x + 1;
    }
  }
  cout << ans << endl;

  return 0;
}

int dfs(int u) {
  vis[u] = 1;
  int ans = 0;
  for (int v : g[u]) {
    if (v == u)
      continue;
    ans++;
    if (vis[v])
      continue;
    ans += dfs(v);
  }
  return ans;
}

Fixed submission:
#include <bits/stdc++.h>
// #include "stdafx.h"
// #pragma warning(disable : 4996) //_CRT_SECURE_NO_WARNINGS
using namespace std;
#define gc getchar_unlocked
#define fo(i, n) for (i = 0; i < n; i++)
#define Fo(i, k, n) for (i = k; k < n ? i < n : i > n; k < n ? i += 1 : i -= 1)
#define ll long long
#define si(x) scanf("%d", &x)
#define sl(x) scanf("%lld", &x)
#define ss(s) scanf("%s", s)
#define pi(x) printf("%d\n", x)
#define pl(x) printf("%lld\n", x)
#define ps(s) printf("%s\n", s)
#define deb(x) cout << #x << "=" << x << endl
#define deb2(x, y) cout << #x << "=" << x << "," << #y << "=" << y << endl
#define pb push_back
#define mp make_pair
#define F first
#define S second
#define all(x) x.begin(), x.end()
#define clr(x) memset(x, 0, sizeof(x))
#define sortall(x) sort(all(x))
#define tr(it, a) for (auto it = a.begin(); it != a.end(); it++)
#define PI 3.1415926535897932384626
typedef pair<int, int> pii;
typedef pair<ll, ll> pl;
typedef vector<int> vi;
typedef vector<ll> vl;
typedef vector<pii> vpii;
typedef vector<pl> vpl;
typedef vector<vi> vvi;
typedef vector<vl> vvl;
int mpow(int base, int exp);
void ipgraph(int m);
int dfs(int u);
const int mod = 1000000007;
const int N = 3e5, M = N;
//=======================

map<int, vi> g;
int a[N];
int b[N];
map<int, int> vis;

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);
  int i, n, k, j;
  cin >> n;
  int x = 0;
  multiset<int> A;
  fo(i, n) cin >> a[i + 1], x ^= a[i + 1], A.insert(a[i + 1]);
  a[0] = x;
  A.insert(x);
  fo(i, n) {
    cin >> b[i + 1];
    if (A.find(b[i + 1]) == A.end()) {
      cout << -1 << endl;
      return 0;
    }
    A.erase(A.find(b[i + 1]));
  }
  b[0] = *A.begin();
  fo(i, n + 1) { g[b[i]].pb(a[i]); }
  int ans = max(1, dfs(a[0])) - 1;
  if (a[0] == b[0] and ans)
    ans++;
  Fo(i, 1, n + 1) {
    if (!vis[a[i]]) {
      x = dfs(a[i]);
      if (x)
        ans += x + 1;
    }
  }
  cout << ans << endl;

  return 0;
}

int dfs(int u) {
  vis[u] = 1;
  int ans = 0;
  for (int v : g[u]) {
    if (v == u)
      continue;
    ans++;
    if (vis[v])
      continue;
    ans += dfs(v);
  }
  return ans;
}