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  1. #include <bits/stdc++.h> 
  2.  
  3. using namespace std;  
  4.  
  5. typedef long long ll;  
  6. typedef pair<ll, ll> ii;  
  7.  
  8. const int INF = 1e9;  
  9. const ll LINF = 1e18;  
  10.  
  11. ll max_time; 
  12. vector<int> digit;   
  13.  
  14. vector<int> getDigit(ll n) {
  15. 	vector<int> ans; 
  16. 	for (; n > 0; n /= 10) ans.push_back(n % 10); 
  17. 	return ans; 
  18. }
  19.  
  20. // dp = {tổng số lượng số target_digit, số lượng số}
  21. ii memo[19][2][2]; 
  22.  
  23. ii dp(int idx, bool leading, bool smaller, int target_digit) {
  24. 	if (idx == -1) return {0, 1};  
  25.  
  26. 	ii& ans = memo[idx][leading][smaller]; 
  27. 	if (ans.first != -1) return ans;  
  28.  
  29. 	ans = {0, 0}; 
  30. 	int max_digit = (smaller) ? 9 : digit[idx]; 
  31.  
  32. 	for (int i = 0; i <= max_digit; i++) {
  33. 		bool new_leading = leading & (i == 0);  
  34. 		ii next_ans = dp(idx - 1, new_leading, smaller | (i < digit[idx]), target_digit); 
  35. 		ans.first += next_ans.first + (!new_leading && i == target_digit) * next_ans.second; 
  36. 		ans.second += next_ans.second;  
  37. 	} 
  38.  
  39. 	return ans; 
  40. }
  41.  
  42. bool check(ll mid) {
  43. 	digit = getDigit(mid);  
  44.  
  45. 	for (int target_digit = 0; target_digit <= 9; target_digit++) {
  46. 		memset(memo, -1, sizeof memo);
  47. 		ll cnt = dp(digit.size() - 1, 1, 0, target_digit).first; 
  48. 		if (cnt > max_time) return false;  
  49. 	}
  50.  
  51. 	return true; 
  52. }
  53.  
  54. int main() {
  55. 	ios::sync_with_stdio(false); 
  56. 	cin.tie(nullptr); 	
  57. 	cin >> max_time;  
  58.  
  59. 	ll l = 0, r = 1e18, ans = -1; 
  60.  
  61. 	while (l <= r) {
  62. 		ll mid = (l + r) >> 1; 
  63.  
  64. 		if (check(mid)) {
  65. 			ans = mid;  
  66. 			l = mid + 1; 
  67. 		}
  68. 		else {
  69. 			r = mid - 1; 
  70. 		}
  71. 	}
  72.  
  73. 	cout << ans << '\n'; 
  74. }
Success #stdin #stdout 0.01s 5272KB
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https://ideone.com/kux8KV
language:
C++14 (gcc 8.3)
created:
1 year ago
visibility:
secret

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