Problem p04048 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <algorithm>
#include <cassert>
#include <climits>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <set>
#include <string>
#include <vector>
using namespace std;
#define MOD 1000000007
#define REP(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define FOR(i, c)                                                              \
  for (decltype((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ll long long
#define all(hoge) (hoge).begin(), (hoge).end()
const long long INF = 1LL << 60;
typedef vector<ll> Array;
typedef vector<Array> Matrix;

struct Edge { // グラフ
  ll to, cap, rev;
  Edge(ll _to, ll _cap, ll _rev) {
    to = _to;
    cap = _cap;
    rev = _rev;
  }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
void add_edge(Graph &G, ll from, ll to,
              ll cap) { // 最大フロー求める Ford-fulkerson
  G[from].push_back(Edge(to, cap, (ll)G[to].size()));
  G[to].push_back(Edge(from, 0, (ll)G[from].size() - 1));
}
ll max_flow_dfs(Graph &G, ll v, ll t, ll f, vector<bool> &used) {
  if (v == t)
    return f;
  used[v] = true;
  for (int i = 0; i < G[v].size(); ++i) {
    Edge &e = G[v][i];
    if (!used[e.to] && e.cap > 0) {
      ll d = max_flow_dfs(G, e.to, t, min(f, e.cap), used);
      if (d > 0) {
        e.cap -= d;
        G[e.to][e.rev].cap += d;
        return d;
      }
    }
  }
  return 0;
}
ll max_flow(Graph &G, ll s, ll t) {
  ll flow = 0;
  for (;;) {
    vector<bool> used(G.size());
    REP(i, used.size()) used[i] = false;
    ll f = max_flow_dfs(G, s, t, INF, used);
    if (f == 0) {
      return flow;
    }
    flow += f;
  }
}

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

class UnionFind {
  vector<int> data;

public:
  UnionFind(int size) : data(size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (data[y] < data[x])
        swap(x, y);
      data[x] += data[y];
      data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
  int size(int x) { return -data[root(x)]; }
};

// 約数求める //約数
void divisor(ll n, vector<ll> &ret) {
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(ret.begin(), ret.end());
}
// 階乗
long long factorial(long long n, long long mod) {
  long long ret = 1;
  for (long long i = 1; i <= n; i++) {
    ret = (ret * i) % mod;
  }
  return ret;
}
// モジュラ逆数
long long inv_mod(long long n, long long mod) {
  long long a = n % mod, b = mod - 2, ret = 1;
  while (b > 0) {
    if (b & 1)
      ret = (ret * a) % mod;
    a = (a * a) % mod;
    b >>= 1;
  }
  return ret;
}

long long nPr(long long n, long long r, long long mod) {
  long long ret = 1;
  for (long long i = n; i >= n - r + 1; i--) {
    ret = ret * (i % mod) % mod;
  }
  return ret;
}

long long nCr(long long n, long long r, long long mod) {
  return nPr(n, r, mod) * inv_mod(factorial(r, mod), mod) % mod;
}

bool compare_by_b(pair<ll, ll> a, pair<ll, ll> b) { // 降順second
  if (a.second != b.second) {
    return a.second > b.second;
  } else {
    return a.first > b.first;
  }
}

bool compare_by_a(pair<ll, ll> a, pair<ll, ll> b) { // 降順first
  if (a.first != b.first) {
    return a.first > b.first;
  } else {
    return a.second > b.second;
  }
}

ll gcd(ll m, ll n) {
  if (n == 0)
    return m;
  return gcd(n, m % n);
} // gcd

int main() {
  ll n, x;
  cin >> n >> x;
  ll side = n - x;
  ll ans = x;
  while (1) {
    if (x % side == 0)
      break;
    n = n % side;
    x = x % side;
    side = side - n;
    ans += n;
  }
  cout << ans * 3;

  return 0;
}


Fixed submission:
#include <algorithm>
#include <cassert>
#include <climits>
#include <cmath>
#include <cstring>
#include <iomanip>
#include <iostream>
#include <map>
#include <queue>
#include <set>
#include <set>
#include <string>
#include <vector>
using namespace std;
#define MOD 1000000007
#define REP(i, n) for (int(i) = 0; (i) < (n); (i)++)
#define FOR(i, c)                                                              \
  for (decltype((c).begin()) i = (c).begin(); i != (c).end(); ++i)
#define ll long long
#define all(hoge) (hoge).begin(), (hoge).end()
const long long INF = 1LL << 60;
typedef vector<ll> Array;
typedef vector<Array> Matrix;

struct Edge { // グラフ
  ll to, cap, rev;
  Edge(ll _to, ll _cap, ll _rev) {
    to = _to;
    cap = _cap;
    rev = _rev;
  }
};
typedef vector<Edge> Edges;
typedef vector<Edges> Graph;
void add_edge(Graph &G, ll from, ll to,
              ll cap) { // 最大フロー求める Ford-fulkerson
  G[from].push_back(Edge(to, cap, (ll)G[to].size()));
  G[to].push_back(Edge(from, 0, (ll)G[from].size() - 1));
}
ll max_flow_dfs(Graph &G, ll v, ll t, ll f, vector<bool> &used) {
  if (v == t)
    return f;
  used[v] = true;
  for (int i = 0; i < G[v].size(); ++i) {
    Edge &e = G[v][i];
    if (!used[e.to] && e.cap > 0) {
      ll d = max_flow_dfs(G, e.to, t, min(f, e.cap), used);
      if (d > 0) {
        e.cap -= d;
        G[e.to][e.rev].cap += d;
        return d;
      }
    }
  }
  return 0;
}
ll max_flow(Graph &G, ll s, ll t) {
  ll flow = 0;
  for (;;) {
    vector<bool> used(G.size());
    REP(i, used.size()) used[i] = false;
    ll f = max_flow_dfs(G, s, t, INF, used);
    if (f == 0) {
      return flow;
    }
    flow += f;
  }
}

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

class UnionFind {
  vector<int> data;

public:
  UnionFind(int size) : data(size, -1) {}
  bool unionSet(int x, int y) {
    x = root(x);
    y = root(y);
    if (x != y) {
      if (data[y] < data[x])
        swap(x, y);
      data[x] += data[y];
      data[y] = x;
    }
    return x != y;
  }
  bool findSet(int x, int y) { return root(x) == root(y); }
  int root(int x) { return data[x] < 0 ? x : data[x] = root(data[x]); }
  int size(int x) { return -data[root(x)]; }
};

// 約数求める //約数
void divisor(ll n, vector<ll> &ret) {
  for (ll i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      ret.push_back(i);
      if (i * i != n)
        ret.push_back(n / i);
    }
  }
  sort(ret.begin(), ret.end());
}
// 階乗
long long factorial(long long n, long long mod) {
  long long ret = 1;
  for (long long i = 1; i <= n; i++) {
    ret = (ret * i) % mod;
  }
  return ret;
}
// モジュラ逆数
long long inv_mod(long long n, long long mod) {
  long long a = n % mod, b = mod - 2, ret = 1;
  while (b > 0) {
    if (b & 1)
      ret = (ret * a) % mod;
    a = (a * a) % mod;
    b >>= 1;
  }
  return ret;
}

long long nPr(long long n, long long r, long long mod) {
  long long ret = 1;
  for (long long i = n; i >= n - r + 1; i--) {
    ret = ret * (i % mod) % mod;
  }
  return ret;
}

long long nCr(long long n, long long r, long long mod) {
  return nPr(n, r, mod) * inv_mod(factorial(r, mod), mod) % mod;
}

bool compare_by_b(pair<ll, ll> a, pair<ll, ll> b) { // 降順second
  if (a.second != b.second) {
    return a.second > b.second;
  } else {
    return a.first > b.first;
  }
}

bool compare_by_a(pair<ll, ll> a, pair<ll, ll> b) { // 降順first
  if (a.first != b.first) {
    return a.first > b.first;
  } else {
    return a.second > b.second;
  }
}

ll gcd(ll m, ll n) {
  if (n == 0)
    return m;
  return gcd(n, m % n);
} // gcd

int main() {
  ll n, x;
  cin >> n >> x;

  cout << 3 * (n - gcd(n, x));

  return 0;
}