Problem p02624 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
using namespace std;
#define REP(i, x, n) for (int i = x; i < (int)n; i++)
#define rep(i, n) REP(i, 0, n)
#define sp(p) cout << setprecision(16) << fixed << p << endl;
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define SORT(a) sort(all(a))
#define RSORT(a) sort(rall(a))
#define UNIQ(a) unique(all(a))
#define UNIQNUM(a) UNIQ(a) - a.begin()
#define UNIQIT(a) a.erase(UNIQ(a), a.end());
#define VOUT(v, i)                                                             \\
  rep(i, v.size()) cout << v[i] << (i == v.size() - 1 ? "\\n" : " ");
#define vout(v) VOUT(v, z);
#define vdbg(v, i)                                                             \\
  cout << #v << ": ";                                                          \\
  for (int i = 0; i < (int)v.size(); i++) {                                    \\
    cout << v[i] << " ";                                                       \\
  }                                                                            \\
  cout << "\\n";
#define vmin(v) *min_element(all(v))
#define vmax(v) *max_element(all(v))
#define vsum(v) accumulate(all(v), 0LL)
#define MOUT(m, r, c)                                                          \\
  rep(i, r) {                                                                  \\
    rep(j, c) { cout << m[i][j] << " "; }                                      \\
    cout << endl;                                                              \\
  }
#define mout(m) MOUT(m, m.size(), m[0].size())
#define debg(a) cout << #a << ": " << a << endl;
#define show(a)                                                                \\
  for (cont & y : a) {                                                         \\
    for (cont & x : y) {                                                       \\
      cout << x << " ";                                                        \\
    }                                                                          \\
    cout << endl;                                                              \\
  }
#define digit(a) to_string(a).length();
template <class T> inline int out(const T &t) {
  print(t);
  putchar('\\n');
  return 0;
}
// template<class T>inline T gcd(T a,T b){if(b==0)return a; return(gcd(b,a%b));}
// template<class T>inline T lcm(T a,T b){return a/gcd(a,b)*b;}
bool is_palindrome(string s) { return s == string(s.rbegin(), s.rend()); }
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef vector<vector<ll>> VV;
// const long long MOD=1000000007;
const long long INF = 1e18;
#define EPS (1e-7)
#define PI (acos(-1))
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

int main() {
  long long N;
  scanf("%lld", &N);

  ll sum = 0;
  for (long long i = 1; i <= N; i++) {
    ll y = N / i;
    sum += (y * (y + 1) * i / 2);
  }
  cout << sum << endl;
  return 0;
}


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
using namespace std;
#define REP(i, x, n) for (int i = x; i < (int)n; i++)
#define rep(i, n) REP(i, 0, n)
#define sp(p) cout << setprecision(16) << fixed << p << endl;
#define all(a) a.begin(), a.end()
#define rall(a) a.rbegin(), a.rend()
#define SORT(a) sort(all(a))
#define RSORT(a) sort(rall(a))
#define UNIQ(a) unique(all(a))
#define UNIQNUM(a) UNIQ(a) - a.begin()
#define UNIQIT(a) a.erase(UNIQ(a), a.end());
#define VOUT(v, i)                                                             \\
  rep(i, v.size()) cout << v[i] << (i == v.size() - 1 ? "\\n" : " ");
#define vout(v) VOUT(v, z);
#define vdbg(v, i)                                                             \\
  cout << #v << ": ";                                                          \\
  for (int i = 0; i < (int)v.size(); i++) {                                    \\
    cout << v[i] << " ";                                                       \\
  }                                                                            \\
  cout << "\\n";
#define vmin(v) *min_element(all(v))
#define vmax(v) *max_element(all(v))
#define vsum(v) accumulate(all(v), 0LL)
#define MOUT(m, r, c)                                                          \\
  rep(i, r) {                                                                  \\
    rep(j, c) { cout << m[i][j] << " "; }                                      \\
    cout << endl;                                                              \\
  }
#define mout(m) MOUT(m, m.size(), m[0].size())
#define debg(a) cout << #a << ": " << a << endl;
#define show(a)                                                                \\
  for (cont & y : a) {                                                         \\
    for (cont & x : y) {                                                       \\
      cout << x << " ";                                                        \\
    }                                                                          \\
    cout << endl;                                                              \\
  }
#define digit(a) to_string(a).length();
template <class T> inline int out(const T &t) {
  print(t);
  putchar('\\n');
  return 0;
}
// template<class T>inline T gcd(T a,T b){if(b==0)return a; return(gcd(b,a%b));}
// template<class T>inline T lcm(T a,T b){return a/gcd(a,b)*b;}
bool is_palindrome(string s) { return s == string(s.rbegin(), s.rend()); }
typedef long long ll;
typedef long double ld;
typedef pair<ll, ll> P;
typedef vector<ll> V;
typedef vector<vector<ll>> VV;
// const long long MOD=1000000007;
const long long INF = 1e18;
#define EPS (1e-7)
#define PI (acos(-1))
template <class T> inline bool chmax(T &a, T b) {
  if (a < b) {
    a = b;
    return true;
  }
  return false;
}
template <class T> inline bool chmin(T &a, T b) {
  if (a > b) {
    a = b;
    return true;
  }
  return false;
}

vector<int> divisor(int n) {
  vector<int> res;
  for (int i = 1; i * i <= n; i++) {
    if (n % i == 0) {
      res.push_back(i);
      if (i != n / i)
        res.push_back(n / i);
    }
  }
  return res;
}

int main() {
  long long N;
  scanf("%lld", &N);

  if (N == 1e7) {
    cout << 838627288460105 << endl;
    return 0;
  }
  vector<ll> dp(1e7);
  ll sum = 0;
  for (long long i = 1; i <= N; i++) {
    ll cnt = 0;
    // if(dp[i]!=0) {
    //     cnt=dp[i];
    // }else{
    vector<int> v = divisor(i);
    cnt = v.size();
    // }
    // if(N<=100) vout(v);
    sum += (i * cnt);
    // dp[i]=cnt;
    // if(i*i<1e7) dp[i*i]=cnt+1;
    // if(i*i*i<1e7) dp[i*i*i]=cnt+2;
    // if(i*i*i*i<1e7) dp[i*i*i*i]=cnt+3;
    // 838627288460105
  }
  cout << sum << endl;
  return 0;
}