Problem p00203 (C++) — buggy submission, verdict: Runtime Error

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for (int i = x; i < n; i++)
template <class T> T RoundOff(T a) { return int(a + .5 - (a < 0)); }
template <class T, class C> void chmax(T &a, C b) {
  if (a < b)
    a = b;
}
template <class T, class C> void chmin(T &a, C b) {
  if (b < a)
    a = b;
}
template <class T, class C> pair<T, C> mp(T a, C b) { return make_pair(a, b); }

int main() {
  int X, Y;
  while (cin >> X >> Y && X) {
    vector<vint> field(Y + 1, vint(X, 0)), dp(Y + 1, vint(X, 0));
    rep(y, Y) rep(x, X) cin >> field[y][x];

    fill(ALL(dp[0]), 1);
    rep(y, Y) rep(x, X) {
      // y, x ツつゥツづァツづ個配ツづゥDP
      if (field[y][x] == 1)
        continue;

      if (field[y][x] == 2 || y + 1 == Y) {
        dp[min(y + 2, Y)][x] += dp[y][x];
      } else {
        int dx[] = {-1, 1};

        dp[y + 1][x] += dp[y][x];
        rep(i, 2) {
          int nx = x + dx[i];
          if (0 <= nx && nx < X && field[y + 1][nx] != 2)
            dp[y + 1][nx] += dp[y][x];
        }
      }
    }

    cout << accumulate(ALL(dp[Y]), 0) << endl;
  }
}

Error: 0

Fixed submission:

#include <algorithm>
#include <bitset>
#include <cassert>
#include <cctype>
#include <cmath>
#include <complex>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <ctime>
#include <fstream>
#include <iomanip>
#include <iostream>
#include <iterator>
#include <list>
#include <map>
#include <numeric>
#include <queue>
#include <set>
#include <sstream>
#include <stack>
#include <string>
#include <utility>
#include <vector>
using namespace std;
typedef long long ll;
const double EPS = 1e-9;
typedef vector<int> vint;
typedef pair<int, int> pint;
#define rep(i, n) REP(i, 0, n)
#define ALL(v) v.begin(), v.end()
#define MSG(a) cout << #a << " " << a << endl;
#define REP(i, x, n) for (int i = x; i < n; i++)
template <class T> T RoundOff(T a) { return int(a + .5 - (a < 0)); }
template <class T, class C> void chmax(T &a, C b) {
  if (a < b)
    a = b;
}
template <class T, class C> void chmin(T &a, C b) {
  if (b < a)
    a = b;
}
template <class T, class C> pair<T, C> mp(T a, C b) { return make_pair(a, b); }

int main() {
  int X, Y;
  while (cin >> X >> Y && X) {
    vector<vint> field(Y, vint(X, 0)), dp(Y, vint(X, 0));
    rep(y, Y) rep(x, X) cin >> field[y][x];

    rep(x, X) dp[0][x] = !field[0][x];

    REP(y, 1, Y) rep(x, X) {
      if (field[y][x] == 1)
        continue;

      if (1 < y && field[y - 2][x] == 2)
        dp[y][x] = dp[y - 2][x];

      if (field[y][x] == 0) {
        int dx[] = {-1, 0, 1};
        rep(i, 3) {
          int nx = x + dx[i];
          if (0 <= nx && nx < X && field[y - 1][nx] != 2)
            dp[y][x] += dp[y - 1][nx];
        }
      } else {
        dp[y][x] += dp[y - 1][x];
      }
    }

    int res = accumulate(ALL(dp[Y - 1]), 0);
    rep(x, X) res += field[Y - 2][x] == 2 ? dp[Y - 2][x] : 0;
    cout << res << endl;
  }
}