Problem p02719 (C++)

Buggy submission (status: Time Limit Exceeded):
#include <bits/stdc++.h>
#define _USE_MATH_DEFINES
#include <math.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define print(s) cout << s << endl
#define acc(v) accumulate(v.begin(), v.end(), 0)
#define cinv(n, v) rep(i, n) cin >> v[i]
using namespace std;
const int INF = 1e9;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vint;
typedef vector<string> vstr;
typedef vector<char> vchar;
const ll LINF = 1e18;
const ll MOD = 1e9 + 7;
int x_pos[4] = {1, 0, -1, 0}, y_pos[4] = {0, 1, 0, -1};
int ctoi(char c) {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  return 0;
}

char upper(char c) { return c - 0x20; }

char lower(char c) { return c + 0x20; }

void unique_vector(vector<int> &v) {
  sort(all(v));
  v.erase(unique(all(v)), v.end());
}

// n次元配列の初期化。第２引数の型のサイズごとに初期化していく。
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

// ユークリッドの互除法
// 最大公約数
ll gcd(ll x, ll y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}

// 最小公倍数
ll lcm(ll x, ll y) {
  ll g = gcd(x, y);
  return x / g * y;
}

ll myPow(ll x, ll n, ll m) {
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return myPow(x * x % m, n / 2, m);
  else
    return x * myPow(x, n - 1, m) % m;
}

// 素因数分解
map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

int main() {
  ll n, k;
  cin >> n >> k;
  while (true) {
    int before = n;
    n = min(min(n, n % k), abs(n - k));
    if (before == n) {
      cout << n << endl;
      return 0;
    }
  }
}


Fixed submission:
#include <bits/stdc++.h>
#define _USE_MATH_DEFINES
#include <math.h>
#define rep(i, n) for (int i = 0; i < (n); ++i)
#define all(x) x.begin(), x.end()
#define rall(x) x.rbegin(), x.rend()
#define print(s) cout << s << endl
#define acc(v) accumulate(v.begin(), v.end(), 0)
#define cinv(n, v) rep(i, n) cin >> v[i]
using namespace std;
const int INF = 1e9;
typedef long long ll;
typedef pair<int, int> pii;
typedef vector<int> vint;
typedef vector<string> vstr;
typedef vector<char> vchar;
const ll LINF = 1e18;
const ll MOD = 1e9 + 7;
int x_pos[4] = {1, 0, -1, 0}, y_pos[4] = {0, 1, 0, -1};
int ctoi(char c) {
  if (c >= '0' && c <= '9') {
    return c - '0';
  }
  return 0;
}

char upper(char c) { return c - 0x20; }

char lower(char c) { return c + 0x20; }

void unique_vector(vector<int> &v) {
  sort(all(v));
  v.erase(unique(all(v)), v.end());
}

// n次元配列の初期化。第２引数の型のサイズごとに初期化していく。
template <typename A, size_t N, typename T>
void Fill(A (&array)[N], const T &val) {
  std::fill((T *)array, (T *)(array + N), val);
}

// ユークリッドの互除法
// 最大公約数
ll gcd(ll x, ll y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}

// 最小公倍数
ll lcm(ll x, ll y) {
  ll g = gcd(x, y);
  return x / g * y;
}

ll myPow(ll x, ll n, ll m) {
  if (n == 0)
    return 1;
  if (n % 2 == 0)
    return myPow(x * x % m, n / 2, m);
  else
    return x * myPow(x, n - 1, m) % m;
}

// 素因数分解
map<ll, ll> prime_factor(ll n) {
  map<ll, ll> ret;
  for (ll i = 2; i * i <= n; i++) {
    while (n % i == 0) {
      ret[i]++;
      n /= i;
    }
  }
  if (n != 1)
    ret[n] = 1;
  return ret;
}

int main() {
  ll n, k;
  cin >> n >> k;
  cout << min(n % k, k - n % k) << endl;
}