Problem p00450 (C++) — buggy submission, verdict: Runtime Error

#include <bits/stdc++.h>
using namespace std;
#define int long long

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, int> plli;
typedef pair<int, pii> pipii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n); i > 0; i--)
#define rrep2(i, a, b) for (int i = (a); i > b; i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()

const ll mod = 1e9 + 7;
const ll INF = 1 << 30;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const double pi = 3.141592653589793;

int n;

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  while (true) {
    cin >> n;
    if (n == 0)
      break;
    int cntw = 0;
    int cntb = 0;
    int pre = -1;
    vector<int> wr, br;
    rep(i, n) {
      int c;
      cin >> c;
      int wsize = wr.size();
      int bsize = br.size();
      if (i % 2 == 0) {
        if (pre != c) {
          if (c == 1)
            wr.pb(i - 1);
          else
            br.pb(i - 1);
          pre = c;
        }
        if (c == 0)
          cntw++;
        else
          cntb++;
      } else {
        if (c == 0) {
          if (pre != c) {
            cntw += i - wr[wsize - 1];
            cntb -= i - wr[wsize - 1] - 1;
            pre = c;
            if (wr[wsize - 1] == -1)
              br.pb(-1);
            wr.pop_back();
          } else
            cntw++;
        } else {
          if (pre != c) {
            cntb += i - br[bsize - 1];
            cntw -= i - br[bsize - 1] - 1;
            pre = c;
            if (br[bsize - 1] == -1)
              wr.pb(-1);
            br.pop_back();
          } else
            cntb++;
        }
      }
    }
    cout << cntw << endl;
  }
}

Error: 0

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#define int long long

typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, int> plli;
typedef pair<int, pii> pipii;
typedef vector<int> vi;
typedef vector<ll> vll;
typedef vector<vi> vvi;
typedef vector<vvi> vvvi;
typedef vector<pii> vpii;

#define rep(i, n) for (int i = 0; i < (n); i++)
#define rep2(i, a, b) for (int i = (a); i < (b); i++)
#define rrep(i, n) for (int i = (n); i > 0; i--)
#define rrep2(i, a, b) for (int i = (a); i > b; i--)
#define pb push_back
#define fi first
#define se second
#define all(a) (a).begin(), (a).end()

const ll mod = 1e9 + 7;
const ll INF = 1 << 30;
const int dx4[4] = {1, 0, -1, 0};
const int dy4[4] = {0, 1, 0, -1};
const int dx8[8] = {1, 1, 1, 0, 0, -1, -1, -1};
const int dy8[8] = {0, 1, -1, 1, -1, 0, 1, -1};
const double pi = 3.141592653589793;

int n;

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);
  while (true) {
    cin >> n;
    if (n == 0)
      break;
    int cntw = 0;
    int cntb = 0;
    int pre = -1;
    vector<int> wr, br;
    rep(i, n) {
      int c;
      cin >> c;
      int wsize = wr.size();
      int bsize = br.size();
      if (i % 2 == 0) {
        if (pre != c) {
          if (c == 1)
            wr.pb(i - 1);
          else
            br.pb(i - 1);
          pre = c;
        }
        if (c == 0)
          cntw++;
        else
          cntb++;
      } else {
        if (c == 0) {
          if (pre != c) {
            cntw += i - wr[wsize - 1];
            cntb -= i - wr[wsize - 1] - 1;
            pre = c;
            if (wr[wsize - 1] == -1)
              br.pb(-1);
            wr.pop_back();
          } else
            cntw++;
        } else {
          if (pre != c) {
            cntb += i - br[bsize - 1];
            cntw -= i - br[bsize - 1] - 1;
            pre = c;
            if (wr[wsize - 1] == -1)
              br.pb(-1);
            br.pop_back();
          } else
            cntb++;
        }
      }
    }
    cout << cntw << endl;
  }
}