Problem p04034 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
using namespace std;

typedef ostringstream OSS;
typedef istringstream ISS;
typedef long long LL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<VVI> VVVI;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef vector<VVLL> VVVLL;
typedef vector<double> VD;
typedef vector<VD> VVD;
typedef vector<VVD> VVVD;
typedef vector<string> VS;
typedef vector<VS> VVS;
typedef vector<VVS> VVVS;
typedef vector<bool> VB;
typedef vector<VB> VVB;
typedef vector<VVB> VVVB;
typedef vector<PII> VPII;
typedef vector<VPII> VVPII;
typedef vector<VVPII> VVVPII;
typedef vector<PLL> VPLL;
typedef vector<VPLL> VVPLL;
typedef vector<VVPLL> VVVPLL;

typedef unsigned int UI;
typedef vector<UI> VUI;
typedef vector<VUI> VVUI;

#define fst first
#define snd second
// #define Y first
// #define X second
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define RANGEBOX(x, y, maxX, maxY)                                             \
  (0 <= (x) && 0 <= (y) && (x) < (maxX) && (y) < (maxY))
#define RANGE(x, l, r) ((l) <= (x) && (x) <= (r))
#define rep(i, N) for (int i = 0; i < (int)(N); i++)
#define rrep(i, N) for (int i = N - 1; i >= 0; i--)
#define REP(i, init, N) for (int i = (init); i < (int)(N); i++)
#define RREP(i, N, last) for (int i = (init - 1); i >= last; i--)
#define MAXUD(orig, target) orig = max(orig, target)
#define MINUD(orig, target) orig = min(orig, target)
#define DUMP(x) cerr << #x << " = " << (x) << endl

template <typename T> inline T fromString(const string &s) {
  T res;
  ISS iss(s);
  iss >> res;
  return res;
};
template <typename T> inline string toString(const T &a) {
  OSS oss;
  oss << a;
  return oss.str();
};

template <typename T = int> inline void dump(vector<T> vs, bool ent = false) {
  rep(i, vs.size()) cout << vs[i] << (i + 1 == vs.size() ? '\n' : ' ');
  if (ent)
    cout << endl;
}
template <typename T = int>
inline void dump(vector<vector<T>> vs, bool ent = false) {
  rep(i, vs.size()) dump<T>(vs[i]);
  if (ent)
    cout << endl;
}

const int INF = 0x3f3f3f3f;
const LL INFL = 0x3f3f3f3f3f3f3f3fLL;
const double DINF = 0x3f3f3f3f;
const int DX[] = {1, 0, -1, 0};
const int DY[] = {0, -1, 0, 1};
const double EPS = 1e-12;
// const double PI   = acos(-1.0);

template <typename T = int> inline T in() {
  T x;
  cin >> x;
  return x;
}
template <typename T = int> inline vector<T> in(int n) {
  vector<T> xs(n);
  rep(i, n) cin >> xs[i];
  return xs;
}
template <typename T = int> inline vector<vector<T>> in(int n, int m) {
  vector<vector<T>> xs(n, vector<T>(m));
  rep(i, n) rep(j, m) cin >> xs[i][j];
  return xs;
}

int main(void) {
  int N = in(), M = in();
  VI xs(N), ys(N);
  rep(i, M) {
    cin >> xs[i] >> ys[i];
    --xs[i];
    --ys[i];
  }

  vector<pair<int, bool>> ts(N);
  rep(i, N) ts[i] = MP(1, false);
  ts[0].snd = true;

  rep(i, M) {
    auto x = xs[i];
    auto y = ys[i];
    ts[x].fst--;
    ts[y].fst++;
    ts[y].snd |= ts[x].snd;
    if (!ts[x].fst)
      ts[x].snd = false;
  }

  cout << count_if(ALL(ts), [](PII t) { return t.snd; }) << endl;

  return 0;
}


Fixed submission:
#include <bits/stdc++.h>
using namespace std;

typedef ostringstream OSS;
typedef istringstream ISS;
typedef long long LL;
typedef pair<int, int> PII;
typedef pair<LL, LL> PLL;
typedef vector<int> VI;
typedef vector<VI> VVI;
typedef vector<VVI> VVVI;
typedef vector<LL> VLL;
typedef vector<VLL> VVLL;
typedef vector<VVLL> VVVLL;
typedef vector<double> VD;
typedef vector<VD> VVD;
typedef vector<VVD> VVVD;
typedef vector<string> VS;
typedef vector<VS> VVS;
typedef vector<VVS> VVVS;
typedef vector<bool> VB;
typedef vector<VB> VVB;
typedef vector<VVB> VVVB;
typedef vector<PII> VPII;
typedef vector<VPII> VVPII;
typedef vector<VVPII> VVVPII;
typedef vector<PLL> VPLL;
typedef vector<VPLL> VVPLL;
typedef vector<VVPLL> VVVPLL;

typedef unsigned int UI;
typedef vector<UI> VUI;
typedef vector<VUI> VVUI;

#define fst first
#define snd second
// #define Y first
// #define X second
#define MP make_pair
#define PB push_back
#define EB emplace_back
#define ALL(x) (x).begin(), (x).end()
#define RALL(x) (x).rbegin(), (x).rend()
#define RANGEBOX(x, y, maxX, maxY)                                             \
  (0 <= (x) && 0 <= (y) && (x) < (maxX) && (y) < (maxY))
#define RANGE(x, l, r) ((l) <= (x) && (x) <= (r))
#define rep(i, N) for (int i = 0; i < (int)(N); i++)
#define rrep(i, N) for (int i = N - 1; i >= 0; i--)
#define REP(i, init, N) for (int i = (init); i < (int)(N); i++)
#define RREP(i, N, last) for (int i = (init - 1); i >= last; i--)
#define MAXUD(orig, target) orig = max(orig, target)
#define MINUD(orig, target) orig = min(orig, target)
#define DUMP(x) cerr << #x << " = " << (x) << endl

template <typename T> inline T fromString(const string &s) {
  T res;
  ISS iss(s);
  iss >> res;
  return res;
};
template <typename T> inline string toString(const T &a) {
  OSS oss;
  oss << a;
  return oss.str();
};

template <typename T = int> inline void dump(vector<T> vs, bool ent = false) {
  rep(i, vs.size()) cout << vs[i] << (i + 1 == vs.size() ? '\n' : ' ');
  if (ent)
    cout << endl;
}
template <typename T = int>
inline void dump(vector<vector<T>> vs, bool ent = false) {
  rep(i, vs.size()) dump<T>(vs[i]);
  if (ent)
    cout << endl;
}

const int INF = 0x3f3f3f3f;
const LL INFL = 0x3f3f3f3f3f3f3f3fLL;
const double DINF = 0x3f3f3f3f;
const int DX[] = {1, 0, -1, 0};
const int DY[] = {0, -1, 0, 1};
const double EPS = 1e-12;
// const double PI   = acos(-1.0);

template <typename T = int> inline T in() {
  T x;
  cin >> x;
  return x;
}
template <typename T = int> inline vector<T> in(int n) {
  vector<T> xs(n);
  rep(i, n) cin >> xs[i];
  return xs;
}
template <typename T = int> inline vector<vector<T>> in(int n, int m) {
  vector<vector<T>> xs(n, vector<T>(m));
  rep(i, n) rep(j, m) cin >> xs[i][j];
  return xs;
}

int main(void) {
  int N = in(), M = in();
  VI xs(M), ys(M);
  rep(i, M) {
    cin >> xs[i] >> ys[i];
    --xs[i];
    --ys[i];
  }

  vector<pair<int, bool>> ts(N);
  rep(i, N) ts[i] = MP(1, false);
  ts[0].snd = true;

  rep(i, M) {
    auto x = xs[i];
    auto y = ys[i];
    ts[x].fst--;
    ts[y].fst++;
    ts[y].snd |= ts[x].snd;
    if (!ts[x].fst)
      ts[x].snd = false;
  }

  cout << count_if(ALL(ts), [](PII t) { return t.snd; }) << endl;

  return 0;
}