Problem p03074 (C++)

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

// types
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<ll> vll;

// macros
#define ALL(a) a.begin(), a.end()
#define SZ(a) ((int)a.size())
#define FI first
#define SE second
#define REP(i, n) for (int i = 0; i < ((int)n); i++)
#define REP1(i, n) for (int i = 1; i < ((int)n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define PB push_back
#define EB emplace_back
#define MP(a, b) make_pair(a, b)
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define Decimal fixed << setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double eps = 1e-10;
const int MOD = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  ll n, k;
  cin >> n >> k;
  string s;
  cin >> s;

  vll v;
  ll cnt = 1;
  char p = s[0];

  if (s[0] == '0')
    v.push_back(0);
  REP1(i, n) {
    if (p != s[i]) {
      v.push_back(cnt);
      cnt = 1;
      p = s[i];
    } else
      cnt++;
  }
  v.push_back(cnt);
  if (s[n - 1] == '0')
    v.push_back(0);

  ll now = 0;
  ll w_size = k * 2 + 1;
  REP(i, w_size)
  now += v[i];

  ll ans = now;
  for (int i = w_size; i + 1 < v.size(); i += 2) {
    now += v[i] + v[i + 1] - (v[i - w_size] + v[i - w_size + 1]);
    ans = max(ans, now);
  }

  cout << ans << endl;
}


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

// types
typedef long long ll;
typedef long double ld;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ld, ld> pdd;
typedef vector<ll> vll;

// macros
#define ALL(a) a.begin(), a.end()
#define SZ(a) ((int)a.size())
#define FI first
#define SE second
#define REP(i, n) for (int i = 0; i < ((int)n); i++)
#define REP1(i, n) for (int i = 1; i < ((int)n); i++)
#define FOR(i, a, b) for (int i = (a); i < (b); i++)
#define PB push_back
#define EB emplace_back
#define MP(a, b) make_pair(a, b)
#define SORT_UNIQUE(c)                                                         \
  (sort(c.begin(), c.end()),                                                   \
   c.resize(distance(c.begin(), unique(c.begin(), c.end()))))
#define GET_POS(c, x) (lower_bound(c.begin(), c.end(), x) - c.begin())
#define Decimal fixed << setprecision(20)
#define INF 1000000000
#define LLINF 1000000000000000000LL

// constants
const int inf = 1e9;
const ll linf = 1LL << 50;
const double eps = 1e-10;
const int MOD = 1e9 + 7;
const int dx[4] = {-1, 0, 1, 0};
const int dy[4] = {0, -1, 0, 1};

int main() {
  ios_base::sync_with_stdio(false);
  cin.tie(NULL);

  ll n, k;
  cin >> n >> k;
  string s;
  cin >> s;

  vll v;
  ll cnt = 1;
  char p = s[0];

  if (s[0] == '0')
    v.push_back(0);
  REP1(i, n) {
    if (p != s[i]) {
      v.push_back(cnt);
      cnt = 1;
      p = s[i];
    } else
      cnt++;
  }
  v.push_back(cnt);
  if (s[n - 1] == '0')
    v.push_back(0);

  ll now = 0;
  ll w_size = min(ll(v.size()), k * 2 + 1);
  REP(i, w_size)
  now += v[i];

  ll ans = now;
  for (int i = w_size; i + 1 < v.size(); i += 2) {
    now += v[i] + v[i + 1] - (v[i - w_size] + v[i - w_size + 1]);
    ans = max(ans, now);
  }

  cout << ans << endl;
}