Problem p02725 (C++)

Buggy submission (status: Runtime Error):
#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast")
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, n) for (int i = 0; i < n; i++)
#define rep2(i, s, f) for (int i = s; i < f; i++)
#define INF 1000000000000000000
#define MOD 1000000007
typedef pair<int, int> P;

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

bool prime(int n) {
  for (int i = 2; i <= sqrt(n); i++) {
    if (n % i == 0)
      return false;
  }
  return n != 1;
}
int gcd(int x, int y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}
int lcm(int x, int y) { return x / gcd(x, y) * y; }
int mod_pow(int n, int p, int m) {
  if (p == 0)
    return 1;
  if (p % 2 == 0) {
    int t = mod_pow(n, p / 2, m);
    return (t * t) % m;
  }
  return n * mod_pow(n, p - 1, m) % m;
}
int extGCD(int a, int b, int &x, int &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  long long d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}
int modinv(int a, int m) {
  int b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
int digit(int x) {
  int cnt = 0;
  while (x > 0) {
    cnt += x % 10;
    x /= 10;
  }
  return cnt;
}
int read() {
  int tmp;
  cin >> tmp;
  return tmp;
}
int xor128() {
  static int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
  int t = (x xor (x << 11));
  x = y;
  y = z;
  z = w;
  return (w = (w xor (w >> 19)) xor (t xor (t >> 8)));
}
map<int, int> factaring(int x) {
  map<int, int> ans;
  int now = 2;
  while (now * now <= x) {
    if (x % now == 0) {
      x /= now;
      ans[now]++;
    } else
      now++;
  }
  if (x != 1)
    ans[x]++;
  return ans;
}
int comb(int n, int k) {
  k = min(k, n - k);
  int x = 1, y = 1;
  rep(i, k) {
    y *= i + 1;
    y %= MOD;
  }
  for (int i = n - k + 1; i <= n; i++) {
    x *= i;
    x %= MOD;
  }
  return x * modinv(y, MOD) % MOD;
}

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

  int k, n;
  int a[100005];
  int ans = INF;
  cin >> k >> n;
  rep(i, n) cin >> a[i];
  a[n] = k + a[0];
  rep(i, n) { chmin(ans, k - (a[i + 1] - a[i])); }
  cout << ans << endl;

  return 0;
}


Fixed submission:
#pragma GCC target("avx")
#pragma GCC optimize("O3")
#pragma GCC optimize("unroll-loops")
#pragma GCC target("sse,sse2,sse3,ssse3,sse4,popcnt,abm,mmx,avx,tune=native")
#pragma GCC optimize("Ofast")
#define _USE_MATH_DEFINES
#include <bits/stdc++.h>
using namespace std;
#define int long long
#define rep(i, n) for (int i = 0; i < n; i++)
#define rep2(i, s, f) for (int i = s; i < f; i++)
#define INF 1000000000000000000
#define MOD 1000000007
typedef pair<int, int> P;

template <class T> bool chmax(T &a, const T &b) {
  if (a < b) {
    a = b;
    return 1;
  }
  return 0;
}
template <class T> bool chmin(T &a, const T &b) {
  if (b < a) {
    a = b;
    return 1;
  }
  return 0;
}

bool prime(int n) {
  for (int i = 2; i <= sqrt(n); i++) {
    if (n % i == 0)
      return false;
  }
  return n != 1;
}
int gcd(int x, int y) {
  if (y == 0)
    return x;
  return gcd(y, x % y);
}
int lcm(int x, int y) { return x / gcd(x, y) * y; }
int mod_pow(int n, int p, int m) {
  if (p == 0)
    return 1;
  if (p % 2 == 0) {
    int t = mod_pow(n, p / 2, m);
    return (t * t) % m;
  }
  return n * mod_pow(n, p - 1, m) % m;
}
int extGCD(int a, int b, int &x, int &y) {
  if (b == 0) {
    x = 1;
    y = 0;
    return a;
  }
  long long d = extGCD(b, a % b, y, x);
  y -= a / b * x;
  return d;
}
int modinv(int a, int m) {
  int b = m, u = 1, v = 0;
  while (b) {
    long long t = a / b;
    a -= t * b;
    swap(a, b);
    u -= t * v;
    swap(u, v);
  }
  u %= m;
  if (u < 0)
    u += m;
  return u;
}
int digit(int x) {
  int cnt = 0;
  while (x > 0) {
    cnt += x % 10;
    x /= 10;
  }
  return cnt;
}
int read() {
  int tmp;
  cin >> tmp;
  return tmp;
}
int xor128() {
  static int x = 123456789, y = 362436069, z = 521288629, w = 88675123;
  int t = (x xor (x << 11));
  x = y;
  y = z;
  z = w;
  return (w = (w xor (w >> 19)) xor (t xor (t >> 8)));
}
map<int, int> factaring(int x) {
  map<int, int> ans;
  int now = 2;
  while (now * now <= x) {
    if (x % now == 0) {
      x /= now;
      ans[now]++;
    } else
      now++;
  }
  if (x != 1)
    ans[x]++;
  return ans;
}
int comb(int n, int k) {
  k = min(k, n - k);
  int x = 1, y = 1;
  rep(i, k) {
    y *= i + 1;
    y %= MOD;
  }
  for (int i = n - k + 1; i <= n; i++) {
    x *= i;
    x %= MOD;
  }
  return x * modinv(y, MOD) % MOD;
}

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

  int k, n;
  int a[200005];
  int ans = INF;
  cin >> k >> n;
  rep(i, n) cin >> a[i];
  a[n] = k + a[0];
  rep(i, n) { chmin(ans, k - (a[i + 1] - a[i])); }
  cout << ans << endl;

  return 0;
}