Problem p03069 (C++)

Buggy submission (status: Runtime Error):
// #include "bits/stdc++.h"

#define _USE_MATH_DEFINES
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <functional>
#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;

#define rep(i, a, b) for (int i = (a), i##_len = (b); i < i##_len; i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define all(c) begin(c), end(c)

#define int ll
#define SZ(x) ((int)(x).size())
#define pb push_back
#define mp make_pair

// typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ll, int> pli;
typedef pair<double, double> pdd;
typedef vector<vector<int>> mat;

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)1e9 + 7;
const double EPS = 1e-9;

int sum[100010][2];

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int N;
  string S;

  cin >> N >> S;
  rep(i, 0, N) {
    sum[i][S[i] == '#' ? 0 : 1]++;
    if (0 < i) {
      rep(j, 0, 2) { sum[i][j] += sum[i - 1][j]; }
    }
  }

  int ans = INF;
  rep(i, 0, N + 1) {
    if (i == 0) {
      chmin(ans, sum[N - 1][1]);
    } else if (i == N) {
      chmin(ans, sum[N - 1][0]);
    } else {
      chmin(ans, sum[N - 1][1] - sum[i - 1][1] + sum[i - 1][0]);
    }
  }

  cout << ans << endl;

  return 0;
}

Fixed submission:
// #include "bits/stdc++.h"

#define _USE_MATH_DEFINES
#include <algorithm>
#include <cmath>
#include <cstdio>
#include <cstdlib>
#include <cstring>
#include <deque>
#include <functional>
#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;

#define rep(i, a, b) for (int i = (a), i##_len = (b); i < i##_len; i++)
#define rrep(i, a, b) for (int i = (b)-1; i >= (a); i--)
#define all(c) begin(c), end(c)

#define int ll
#define SZ(x) ((int)(x).size())
#define pb push_back
#define mp make_pair

// typedef unsigned long long ull;
typedef long long ll;
typedef pair<int, int> pii;
typedef pair<ll, ll> pll;
typedef pair<ll, int> pli;
typedef pair<double, double> pdd;
typedef vector<vector<int>> mat;

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return true;
  }
  return false;
}

const int INF =
    sizeof(int) == sizeof(long long) ? 0x3f3f3f3f3f3f3f3fLL : 0x3f3f3f3f;
const int MOD = (int)1e9 + 7;
const double EPS = 1e-9;

int sum[200010][2];

signed main() {
  cin.tie(0);
  ios::sync_with_stdio(false);

  int N;
  string S;

  cin >> N >> S;
  rep(i, 0, N) {
    sum[i][S[i] == '#' ? 0 : 1]++;
    if (0 < i) {
      rep(j, 0, 2) { sum[i][j] += sum[i - 1][j]; }
    }
  }

  int ans = INF;
  rep(i, 0, N + 1) {
    if (i == 0) {
      chmin(ans, sum[N - 1][1]);
    } else if (i == N) {
      chmin(ans, sum[N - 1][0]);
    } else {
      chmin(ans, sum[N - 1][1] - sum[i - 1][1] + sum[i - 1][0]);
    }
  }

  cout << ans << endl;

  return 0;
}