Problem p03137 (C++)

Buggy submission (status: Runtime Error):
#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(a, b) for (int a = 0; a < (b); ++a)
#define REP1(i, n) for (int i = 1; i <= (n); ++i)
#define debug(x) cerr << #x << ": " << x << '\n'
#define all(x) (x).begin(), (x).end()
#define YES() printf("YES\n")
#define NO() printf("NO\n")
#define isYES(x) printf("%s\n", (x) ? "YES" : "NO")
#define Yes() printf("Yes\n")
#define No() printf("No\n")
#define isYes(x) printf("%s\n", (x) ? "Yes" : "No")
#define SZ(x) ((int)(x).size())
#define pb push_back
#define mp make_pair
#define INF (1 << 29)
#define Sp(p) cout << setprecision(25) << fixed << p << endl
#define vi vector<int>
#define vl vector<ll>
#define vii vector<vector<int>>
#define vll vector<vector<ll>>
#define vs vector<string>
#define pii pair<int, int>
#define pis pair<int, string>
#define psi pair<string, int>
#define pll pair<ll, ll>
#define X first
#define Y second
using namespace std;
typedef pair<int, int> P;
typedef pair<ll, ll> LP;
typedef pair<int, P> PP;
typedef pair<ll, LP> LPP;

template <class T = int> T in() {
  T x;
  cin >> x;
  return (x);
}
template <class T> void print(T &x) { cout << x << '\n'; }

const int MOD = (int)1e9 + 7;
const int MAX = 510000;
ll fac[MAX], finv[MAX], inv[MAX];
void COMint() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
ll COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  if (a > b) {
    swap(a, b);
  }
  return gcd(a, b % a);
}
ll lcm(ll a, ll b) {
  ll g;
  g = gcd(a, b);
  return a * b / g;
}
bool compare_by_b(pair<int, int> a, pair<int, int> b) {
  if (a.second != b.second) {
    return a.second < b.second;
  } else {
    return a.first < b.first;
  }
}

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

ll RS(ll N, ll P, ll M) {
  if (P == 0) {
    return 1;
  } else {
    if (P % 2 == 0) {
      ll t = RS(N, P / 2, M);
      return t * t % M;
    } else {
      return N * RS(N, P - 1, M) % M;
    }
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int N = in();
  int M = in();
  vector<int> vec(M);
  REP(i, M) { cin >> vec[i]; }

  if (M == 1) {
    cout << 0 << endl;
    return 0;
  }
  sort(all(vec));
  ll ans = 0;
  ans = vec[vec.size() - 1] - vec[0];
  vector<int> aida(M - 1);
  int now;
  now = vec[0];
  REP(i, M - 1) {
    aida[i] = vec[i + 1] - now;
    now = vec[i + 1];
  }
  sort(all(aida));
  REP(i, N - 1) { ans -= aida[aida.size() - 1 - i]; }
  cout << ans << endl;
  return 0;
}

Fixed submission:
#include <bits/stdc++.h>
#define ll long long
#define ull unsigned long long
#define FOR(i, a, b) for (int i = (a); i < (b); ++i)
#define REP(a, b) for (int a = 0; a < (b); ++a)
#define REP1(i, n) for (int i = 1; i <= (n); ++i)
#define debug(x) cerr << #x << ": " << x << '\n'
#define all(x) (x).begin(), (x).end()
#define YES() printf("YES\n")
#define NO() printf("NO\n")
#define isYES(x) printf("%s\n", (x) ? "YES" : "NO")
#define Yes() printf("Yes\n")
#define No() printf("No\n")
#define isYes(x) printf("%s\n", (x) ? "Yes" : "No")
#define SZ(x) ((int)(x).size())
#define pb push_back
#define mp make_pair
#define INF (1 << 29)
#define Sp(p) cout << setprecision(25) << fixed << p << endl
#define vi vector<int>
#define vl vector<ll>
#define vii vector<vector<int>>
#define vll vector<vector<ll>>
#define vs vector<string>
#define pii pair<int, int>
#define pis pair<int, string>
#define psi pair<string, int>
#define pll pair<ll, ll>
#define X first
#define Y second
using namespace std;
typedef pair<int, int> P;
typedef pair<ll, ll> LP;
typedef pair<int, P> PP;
typedef pair<ll, LP> LPP;

template <class T = int> T in() {
  T x;
  cin >> x;
  return (x);
}
template <class T> void print(T &x) { cout << x << '\n'; }

const int MOD = (int)1e9 + 7;
const int MAX = 510000;
ll fac[MAX], finv[MAX], inv[MAX];
void COMint() {
  fac[0] = fac[1] = 1;
  finv[0] = finv[1] = 1;
  inv[1] = 1;
  for (int i = 2; i < MAX; i++) {
    fac[i] = fac[i - 1] * i % MOD;
    inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
    finv[i] = finv[i - 1] * inv[i] % MOD;
  }
}
ll COM(int n, int k) {
  if (n < k)
    return 0;
  if (n < 0 || k < 0)
    return 0;
  return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
}
ll gcd(ll a, ll b) {
  if (b == 0)
    return a;
  if (a > b) {
    swap(a, b);
  }
  return gcd(a, b % a);
}
ll lcm(ll a, ll b) {
  ll g;
  g = gcd(a, b);
  return a * b / g;
}
bool compare_by_b(pair<int, int> a, pair<int, int> b) {
  if (a.second != b.second) {
    return a.second < b.second;
  } else {
    return a.first < b.first;
  }
}

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

ll RS(ll N, ll P, ll M) {
  if (P == 0) {
    return 1;
  } else {
    if (P % 2 == 0) {
      ll t = RS(N, P / 2, M);
      return t * t % M;
    } else {
      return N * RS(N, P - 1, M) % M;
    }
  }
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  int N = in();
  int M = in();
  vector<int> vec(M);
  REP(i, M) { cin >> vec[i]; }

  if (M == 1 || N >= M) {
    cout << 0 << endl;
    return 0;
  }
  sort(all(vec));
  ll ans = 0;
  ans = vec[vec.size() - 1] - vec[0];
  vector<int> aida(M - 1);
  int now;
  now = vec[0];
  REP(i, M - 1) {
    aida[i] = vec[i + 1] - now;
    now = vec[i + 1];
  }
  sort(all(aida));
  REP(i, N - 1) { ans -= aida[aida.size() - 1 - i]; }
  cout << ans << endl;
  return 0;
}