Problem p03726 (C++)

Buggy submission (status: Runtime Error):
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string.h>
#include <string>
#include <vector>
#define fi first
#define se second
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define gep(i, g, j) for (int i = g.head[j]; i != -1; i = g.e[i].next)
#define each(it, c)                                                            \
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); it++)
#define rng(a) a.begin(), a.end()
#define maxs(x, y) x = max(x, y)
#define mins(x, y) x = min(x, y)
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcount
#define uni(x) x.erase(unique(rng(x)), x.end())
#define snuke srand((unsigned)clock() + (unsigned)time(NULL));
#define df(x) int x = in()
#define dame                                                                   \
  {                                                                            \
    puts("-1");                                                                \
    return 0;                                                                  \
  }
#define show(x) cout << #x << " = " << x << endl;
#define PQ(T) priority_queue<T, vector<T>, greater<T>>
#define bn(x) ((1 << x) - 1)
#define newline puts("")
#define v(T) vector<T>
#define vv(T) vector<vector<T>>
using namespace std;
typedef long long int ll;
typedef unsigned uint;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
inline int in() {
  int x;
  scanf("%d", &x);
  return x;
}
inline void priv(vi a) {
  rep(i, sz(a)) printf("%d%c", a[i], i == sz(a) - 1 ? '\n' : ' ');
}
template <typename T> istream &operator>>(istream &i, vector<T> &v) {
  rep(j, sz(v)) i >> v[j];
  return i;
}
template <typename T> string join(const vector<T> &v) {
  stringstream s;
  rep(i, sz(v)) s << ' ' << v[i];
  return s.str().substr(1);
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  if (sz(v))
    o << join(v);
  return o;
}
template <typename T1, typename T2>
istream &operator>>(istream &i, pair<T1, T2> &v) {
  return i >> v.fi >> v.se;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &o, const pair<T1, T2> &v) {
  return o << v.fi << "," << v.se;
}
const int MX = 100005, INF = 1001001001;
const ll LINF = 1e18;
const double eps = 1e-10;

int main() {
  int n;
  scanf("%d", &n);
  vvi to(n);
  rep(i, n - 1) {
    int a, b;
    scanf("%d%d", &a, &b);
    --a;
    --b;
    to[a].pb(b);
    to[b].pb(a);
  }
  queue<int> q;
  vi deg(n);
  rep(i, n) {
    deg[i] = sz(to[i]);
    if (deg[i] == 1)
      q.push(i);
  }
  while (sz(q)) {
    int v = q.front();
    q.pop();
    deg[v] = -1;
    int nv = -1;
    for (int u : to[v]) {
      if (deg[u] > 0)
        nv = u;
    }
    deg[nv] = -1;
    for (int u : to[nv]) {
      deg[u]--;
      if (deg[u] == 0) {
        puts("First");
        return 0;
      }
      if (deg[u] == 1) {
        q.push(u);
      }
    }
  }
  puts("Second");
  return 0;
}


Fixed submission:
#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <ctime>
#include <deque>
#include <iostream>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string.h>
#include <string>
#include <vector>
#define fi first
#define se second
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define rrep(i, n) for (int i = 1; i <= (n); ++i)
#define drep(i, n) for (int i = (n)-1; i >= 0; --i)
#define gep(i, g, j) for (int i = g.head[j]; i != -1; i = g.e[i].next)
#define each(it, c)                                                            \
  for (__typeof((c).begin()) it = (c).begin(); it != (c).end(); it++)
#define rng(a) a.begin(), a.end()
#define maxs(x, y) x = max(x, y)
#define mins(x, y) x = min(x, y)
#define pb push_back
#define sz(x) (int)(x).size()
#define pcnt __builtin_popcount
#define uni(x) x.erase(unique(rng(x)), x.end())
#define snuke srand((unsigned)clock() + (unsigned)time(NULL));
#define df(x) int x = in()
#define dame                                                                   \
  {                                                                            \
    puts("-1");                                                                \
    return 0;                                                                  \
  }
#define show(x) cout << #x << " = " << x << endl;
#define PQ(T) priority_queue<T, vector<T>, greater<T>>
#define bn(x) ((1 << x) - 1)
#define newline puts("")
#define v(T) vector<T>
#define vv(T) vector<vector<T>>
using namespace std;
typedef long long int ll;
typedef unsigned uint;
typedef unsigned long long ull;
typedef pair<int, int> P;
typedef vector<int> vi;
typedef vector<vi> vvi;
typedef vector<ll> vl;
typedef vector<P> vp;
inline int in() {
  int x;
  scanf("%d", &x);
  return x;
}
inline void priv(vi a) {
  rep(i, sz(a)) printf("%d%c", a[i], i == sz(a) - 1 ? '\n' : ' ');
}
template <typename T> istream &operator>>(istream &i, vector<T> &v) {
  rep(j, sz(v)) i >> v[j];
  return i;
}
template <typename T> string join(const vector<T> &v) {
  stringstream s;
  rep(i, sz(v)) s << ' ' << v[i];
  return s.str().substr(1);
}
template <typename T> ostream &operator<<(ostream &o, const vector<T> &v) {
  if (sz(v))
    o << join(v);
  return o;
}
template <typename T1, typename T2>
istream &operator>>(istream &i, pair<T1, T2> &v) {
  return i >> v.fi >> v.se;
}
template <typename T1, typename T2>
ostream &operator<<(ostream &o, const pair<T1, T2> &v) {
  return o << v.fi << "," << v.se;
}
const int MX = 100005, INF = 1001001001;
const ll LINF = 1e18;
const double eps = 1e-10;

int main() {
  int n;
  scanf("%d", &n);
  vvi to(n);
  rep(i, n - 1) {
    int a, b;
    scanf("%d%d", &a, &b);
    --a;
    --b;
    to[a].pb(b);
    to[b].pb(a);
  }
  queue<int> q;
  vi deg(n);
  rep(i, n) {
    deg[i] = sz(to[i]);
    if (deg[i] == 1)
      q.push(i);
  }
  while (sz(q)) {
    int v = q.front();
    q.pop();
    if (deg[v] < 0) {
      continue;
    }
    deg[v] = -1;
    int nv = -1;
    for (int u : to[v]) {
      if (deg[u] > 0)
        nv = u;
    }
    deg[nv] = -1;
    for (int u : to[nv]) {
      deg[u]--;
      if (deg[u] == 0) {
        puts("First");
        return 0;
      }
      if (deg[u] == 1) {
        q.push(u);
      }
    }
  }
  puts("Second");
  return 0;
}