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  1. #include <bits/stdc++.h>
  2. using namespace std;
  3. #define faster ios_base::sync_with_stdio(false); cin.tie(NULL)
  4. #define Bit(mask , i) ((mask >> i) & 1)
  5. #define fi first
  6. #define se second
  7. #define _LOG2(nl) 31 - __builtin_clz(nl)
  8. #define c_bit(nl) __builtin_popcount(nl)
  9. #define ii pair<int , pair<int , int>>
  10. #define lii pair<long long , pair<int , int>>
  11. #define li pair<long long , int>
  12. #define db double
  13. #define onBit(mask , i) (mask | (1 << i))
  14. #define offBit(mask , i) (mask & (~(1 << i)))
  15.  
  16. long long n;
  17. long long f[12][3][3][3];
  18.  
  19. void inp(){
  20.     cin >> n;
  21. }
  22.  
  23. long long dp(int pos , int lower , int parity , int find_st , string &x){
  24.     if (pos == x.size()){
  25.         return find_st;
  26.     }
  27.  
  28.     if (f[pos][lower][parity][find_st] != -1) return f[pos][lower][parity][find_st];
  29.  
  30.     int fin = 9;
  31.     if (lower) fin = x[pos] - '0';
  32.     long long res = 0;
  33.     for (int i = 0 ; i <= fin ; ++i){
  34.         int j = i % 2;
  35.         if (find_st){
  36.             if (!(j ^ parity))continue;
  37.         }
  38.         int n_lower = 0;
  39.         if (lower == 1 && i == fin) n_lower = 1;
  40.         int n_find_st = 1;
  41.         if (!find_st  && i == 0) n_find_st = 0;
  42.         res += dp(pos + 1 , n_lower , j , n_find_st , x);
  43.     }
  44.     return f[pos][lower][parity][find_st] = res;
  45. }
  46.  
  47. void solve(){
  48.     string s = to_string(n);
  49.     memset(f , -1 , sizeof f);
  50.     cout << dp(0 , 1 , 0 , 0 , s);
  51. }
  52.  
  53. int main(){
  54.     if (fopen("cau3.inp" , "r")){
  55.         freopen("cau3.inp" , "r" , stdin);
  56.         freopen("cau3.out" , "w" , stdout);
  57.     }
  58.     faster;
  59.     inp();
  60.     solve();
  61.     return 0;
  62. }
  63.  
Success #stdin #stdout 0.01s 5288KB
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https://ideone.com/QPkcMx
language:
C++14 (gcc 8.3)
created:
15 hours ago
visibility:
public

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