Problem p02696 (C++) — buggy submission, verdict: Time Limit Exceeded

#include <bits/stdc++.h>
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
//
//     #pragma GCC optimize("unroll-loops")
//     #pragma GCC optimize("Ofast")
//     #pragma GCC optimize("-O3")
//     #pragma GCC optimize("no-stack-protector")
//     #pragma GCC optimize("fast-math")

#define fi first
#define f first
#define se second
#define s second
#define vi_a vector<int> a;
#define p_b push_back
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ll long long
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ld long double
#define pll pair<ll, ll>
#define pii pair<int, int>
#define m_p make_pair
#define fast_io                                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);                                                                 \\
  ios_base::sync_with_stdio(0);
#define all(x) x.begin(), x.end()
#define getfiles                                                               \\
  ifstream cin("input.txt");                                                   \\
  ofstream cout("output.txt");
#define pw(x) (1ll << x)
#define sz(x) (ll) x.size()
#define endl "\\n"
#define rall(x) x.rbegin(), x.rend()
#define len(a) (ll) a.size()
#define rep(x, l, r) for (ll x = l; x < r; x++)
// #define for(int i=0;i<n;i++) for(ll i=0;i<n;i++)
using namespace std;
// using namespace __gnu_pbds;
ld eps = (ld)1 / 1e6;
ll inf = 1e18, mod2 = 998244353, mod1 = 1e9 + 7;
ll sqr(ll a) { return a * a; }
ll qb(ll a) { return a * a * a; }
ll gcd(ll a, ll b) { return !a ? b : gcd(b % a, a); }
ll binpow(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (a * (sqr(binpow(a, b / 2, mod)) % mod)) % mod
                    : sqr(binpow(a, b / 2, mod)) % mod)
           : 1;
}
ll binmult(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (2 * binmult(a, b / 2, mod) + a) % mod
                    : (2 * binmult(a, b / 2, mod)) % mod)
           : 0;
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// const ll to[5]={0,4,6,7,9};
// const ll N=2*1e5+1;
const ll R = 1e4;
// const ll to[7]={1,2,3,1,3,2,1};
const ll tx[4] = {0, 0, -1, 1};
const ll ty[4] = {-1, 1, 0, 0};
const char rev_to[4] = {'E', 'W', 'N', 'S'};
const ll N = 2 * 1e5 + 4;
ll n;
vector<ll> b, c, d, e;
ll mx = 0;
ll m;
void brute(vector<ll> &a, ll indx, ll prev) {
  if (indx == n) {
    ll ans = 0;
    for (ll i = 0; i < sz(b); i++) {
      if (a[c[i]] - a[b[i]] == d[i]) {
        ans += e[i];
      }
    }
    mx = max(mx, ans);
  } else {
    for (ll i = prev; i <= m; i++) {
      a[indx] = i;
      brute(a, indx + 1, i);
    }
  }
}
ll brute(ll a, ll b, ll n) {
  ll mx = -inf;
  ll mx2 = -inf;
  bool ok1 = 1;
  ll pos;
  for (ll i = 0; i <= n; i++) {
    if (mx < (a * i / b) - a * (i / b))
      pos = i;
    mx = max(mx, (a * i / b) - a * (i / b));
    //   if(mx)
    // cout<<(a*i/b)-a*(i/b)<<" ";
  }
  cout << pos << endl;
  return mx;
}
ll solve(ll a, ll b, ll n) {
  if (n >= b) {
    return (a * (b - 1) / b) - a * ((b - 1) / b);
  } else {
    return (a * (n) / b) - a * ((n) / b);
  }
}
void check() {
  auto bd = bind(uniform_int_distribution<ll>(1, 1000), mt19937(time(0)));
  while (1) {
    ll a = bd(), b = bd(), n = bd();
    // ll a=246 ,b=247,n=269;
    cout << "Testing..." << a << " " << b << " " << n << endl;
    ll ans1 = brute(a, b, n), ans2 = solve(a, b, n);
    cout << ans1 << " " << ans2 << endl;
    if (ans1 != ans2) {
      return;
    }
  }
}
signed main() {
  fast_io;
  ll a, b, n;
  cin >> a >> b >> n;
  cout << solve(a, b, n);
  //    check();
  return 0;
}
/*
    n*(m+1)/2*m;
    10321 300 10031//b-1
    300 1003 100 //n
    a>b -  b-1
    a<=b && n<b - n
    a<=b && n>b
    если WA , то чекер говно, поэтому почекай l8 строчку

*/


Error: TLE

Fixed submission:

#include <bits/stdc++.h>
// #include<ext/pb_ds/assoc_container.hpp>
// #include<ext/pb_ds/tree_policy.hpp>
//
//     #pragma GCC optimize("unroll-loops")
//     #pragma GCC optimize("Ofast")
//     #pragma GCC optimize("-O3")
//     #pragma GCC optimize("no-stack-protector")
//     #pragma GCC optimize("fast-math")

#define fi first
#define f first
#define se second
#define s second
#define vi_a vector<int> a;
#define p_b push_back
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ll long long
////////////////////////////////???????????????CHECK THIS
///OUT???????????????//////////////////////////////
#define ld long double
#define pll pair<ll, ll>
#define pii pair<int, int>
#define m_p make_pair
#define fast_io                                                                \\
  cin.tie(0);                                                                  \\
  cout.tie(0);                                                                 \\
  ios_base::sync_with_stdio(0);
#define all(x) x.begin(), x.end()
#define getfiles                                                               \\
  ifstream cin("input.txt");                                                   \\
  ofstream cout("output.txt");
#define pw(x) (1ll << x)
#define sz(x) (ll) x.size()
#define endl "\\n"
#define rall(x) x.rbegin(), x.rend()
#define len(a) (ll) a.size()
#define rep(x, l, r) for (ll x = l; x < r; x++)
// #define for(int i=0;i<n;i++) for(ll i=0;i<n;i++)
using namespace std;
// using namespace __gnu_pbds;
ld eps = (ld)1 / 1e6;
ll inf = 1e18, mod2 = 998244353, mod1 = 1e9 + 7;
ll sqr(ll a) { return a * a; }
ll qb(ll a) { return a * a * a; }
ll gcd(ll a, ll b) { return !a ? b : gcd(b % a, a); }
ll binpow(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (a * (sqr(binpow(a, b / 2, mod)) % mod)) % mod
                    : sqr(binpow(a, b / 2, mod)) % mod)
           : 1;
}
ll binmult(ll a, ll b, ll mod) {
  return b ? (b % 2 ? (2 * binmult(a, b / 2, mod) + a) % mod
                    : (2 * binmult(a, b / 2, mod)) % mod)
           : 0;
}
/////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////////
// const ll to[5]={0,4,6,7,9};
// const ll N=2*1e5+1;
const ll R = 1e4;
// const ll to[7]={1,2,3,1,3,2,1};
const ll tx[4] = {0, 0, -1, 1};
const ll ty[4] = {-1, 1, 0, 0};
const char rev_to[4] = {'E', 'W', 'N', 'S'};
const ll N = 2 * 1e5 + 4;
ll n;
vector<ll> b, c, d, e;
ll mx = 0;
ll m;
void brute(vector<ll> &a, ll indx, ll prev) {
  if (indx == n) {
    ll ans = 0;
    for (ll i = 0; i < sz(b); i++) {
      if (a[c[i]] - a[b[i]] == d[i]) {
        ans += e[i];
      }
    }
    mx = max(mx, ans);
  } else {
    for (ll i = prev; i <= m; i++) {
      a[indx] = i;
      brute(a, indx + 1, i);
    }
  }
}
signed main() {
  fast_io;
  ll a, b, n;
  cin >> a >> b >> n;
  map<ll, bool> mp;
  ll mx = -inf;
  ll mx2 = -inf;
  bool ok1 = 1;
  for (ll i = 0; i <= n; i++) {
    // cout<<(a*i/b)-a*(i/b)<<" ";
    mx = max(mx, (a * i / b) - a * (i / b));
    if ((a * i / b) - a * (i / b) < mx)
      ok1 = 0;
    if (ok1) {
      mx2 = max(mx2, mx);
      // break;
    } else {
      break;
    }
    // if(mp[(a*i/b)-a*(i/b)]) break;
  }
  //    for(ll i=0;i<n;i++){
  //        cout<<(a*i/b)-a*(i/b)<<" ";
  //        mx=max(mx,(a*i/b)-a*(i/b));
  //        mp[(a*i/b)-a*(i/b)]=1;
  //       // if(mp[(a*i/b)-a*(i/b)]) break;
  //    }
  cout << mx2;
  return 0;
}
/*
    n*(m+1)/2*m;
    если WA , то чекер говно, поэтому почекай l8 строчку

*/