Problem p03575 (C++)

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

#include <ext/pb_ds/assoc_container.hpp> //required
#include <ext/pb_ds/tree_policy.hpp>     //required

using namespace __gnu_pbds;
using namespace std;

template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// find_by_order(k)  returns iterator to kth element starting from 0;
// order_of_key(k) returns count of elements strictly smaller than k;
typedef long long ll;
typedef vector<ll> VL;
typedef vector<int> VI;
typedef pair<ll, ll> PLL;
typedef pair<int, int> PII;
#define pb push_back

#define F first
#define S second
#define SZ(a) int((a).size())
#define ALL(a) a.begin(), a.end()
#define fr(i, x, y) for (int i = x; i < y; i++)
#define frr(i, x, y) for (int i = x - 1; i >= y; i--)
#define inf 1e18 + 1
#define IOS                                                                    \
  ios::sync_with_stdio(0);                                                     \
  cin.tie(0);                                                                  \
  cout.tie(0);
const int mod = 1000000007;
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll power(ll a, ll b) {
  ll ans = 1;
  while (b != 0) {
    if (b & 1) {
      ans *= a;
    }
    a = a * a;
    b >>= 1;
  }
  return ans;
}
ll powerm(ll a, ll b) {
  ll ans = 1;
  while (b != 0) {
    if (b & 1) {
      ans *= a;
      ans %= mod;
    }
    a = a * a;
    a %= mod;
    b >>= 1;
  }
  return ans % mod;
}
// string to integer stoi()
// string to long long stoll()
// string.substr(position,length);
// integer to string to_string();
vector<VL> adj;
VL visit2;
void dfs(ll v) {
  visit2[v] = 1;
  for (auto i : adj[v]) {
    if (visit2[i] == -1) {
      dfs(i);
    }
  }
  return;
}
void solve() {

  ll n, m;
  cin >> n >> m;
  vector<PLL> arr(n);
  fr(i, 0, m) {
    cin >> arr[i].F >> arr[i].S;
    arr[i].F--;
    arr[i].S--;
  }
  ll bridge = 0;
  fr(i, 0, m) {
    adj.clear();
    visit2.clear();
    adj.assign(n, VL());
    bool fg = false;
    fr(j, 0, m) {
      if (i != j) {
        adj[arr[j].F].pb(arr[j].S);
        adj[arr[j].S].pb(arr[j].F);
      }
    }
    visit2.assign(n, -1);
    dfs(0);
    fr(k, 0, n) {
      if (visit2[k] == -1) {
        fg = true;
      }
    }
    if (fg) {
      bridge++;
    }
  }
  cout << bridge << endl;
  return;
}
int main() {
  IOS;
  ll t = 1;
  // cin>>t;
  while (t--) {
    // cout<<"Case #"<<pp-t<<":\n";
    solve();
  }
  return 0;
}
/* stuff you should look for
 * int overflow, array bounds
 * special cases (n=1?)
 * do smth instead of nothing and stay organized
 * WRITE STUFF DOWN
 */
/*
recursion - matrix exponential

*/
// BITMASK:
// 1)When some constrall is of the order of 15-20, think of bitmask DP.
// 2)When some constrall is around 40, try out meet in the middle
// 3) See Strings,palindromes,prefix,suffix etc -> KMP,Z algorithm

Fixed submission:
#include <bits/stdc++.h>

#include <ext/pb_ds/assoc_container.hpp> //required
#include <ext/pb_ds/tree_policy.hpp>     //required

using namespace __gnu_pbds;
using namespace std;

template <typename T>
using ordered_set =
    tree<T, null_type, less<T>, rb_tree_tag, tree_order_statistics_node_update>;
// find_by_order(k)  returns iterator to kth element starting from 0;
// order_of_key(k) returns count of elements strictly smaller than k;
typedef long long ll;
typedef vector<ll> VL;
typedef vector<int> VI;
typedef pair<ll, ll> PLL;
typedef pair<int, int> PII;
#define pb push_back

#define F first
#define S second
#define SZ(a) int((a).size())
#define ALL(a) a.begin(), a.end()
#define fr(i, x, y) for (int i = x; i < y; i++)
#define frr(i, x, y) for (int i = x - 1; i >= y; i--)
#define inf 1e18 + 1
#define IOS                                                                    \
  ios::sync_with_stdio(0);                                                     \
  cin.tie(0);                                                                  \
  cout.tie(0);
const int mod = 1000000007;
ll gcd(ll a, ll b) { return b ? gcd(b, a % b) : a; }
ll power(ll a, ll b) {
  ll ans = 1;
  while (b != 0) {
    if (b & 1) {
      ans *= a;
    }
    a = a * a;
    b >>= 1;
  }
  return ans;
}
ll powerm(ll a, ll b) {
  ll ans = 1;
  while (b != 0) {
    if (b & 1) {
      ans *= a;
      ans %= mod;
    }
    a = a * a;
    a %= mod;
    b >>= 1;
  }
  return ans % mod;
}
// string to integer stoi()
// string to long long stoll()
// string.substr(position,length);
// integer to string to_string();
vector<VL> adj;
VL visit2;
void dfs(ll v) {
  visit2[v] = 1;
  for (auto i : adj[v]) {
    if (visit2[i] == -1) {
      dfs(i);
    }
  }
  return;
}
void solve() {

  ll n, m;
  cin >> n >> m;
  vector<PLL> arr(m);
  fr(i, 0, m) {
    cin >> arr[i].F >> arr[i].S;
    arr[i].F--;
    arr[i].S--;
  }
  ll bridge = 0;
  fr(i, 0, m) {
    adj.clear();
    visit2.clear();
    adj.assign(n, VL());
    bool fg = false;
    fr(j, 0, m) {
      if (i != j) {
        adj[arr[j].F].pb(arr[j].S);
        adj[arr[j].S].pb(arr[j].F);
      }
    }
    visit2.assign(n, -1);
    dfs(0);
    fr(k, 0, n) {
      if (visit2[k] == -1) {
        fg = true;
      }
    }
    if (fg) {
      bridge++;
    }
  }
  cout << bridge << endl;
  return;
}
int main() {
  IOS;
  ll t = 1;
  // cin>>t;
  while (t--) {
    // cout<<"Case #"<<pp-t<<":\n";
    solve();
  }
  return 0;
}
/* stuff you should look for
 * int overflow, array bounds
 * special cases (n=1?)
 * do smth instead of nothing and stay organized
 * WRITE STUFF DOWN
 */
/*
recursion - matrix exponential

*/
// BITMASK:
// 1)When some constrall is of the order of 15-20, think of bitmask DP.
// 2)When some constrall is around 40, try out meet in the middle
// 3) See Strings,palindromes,prefix,suffix etc -> KMP,Z algorithm