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  1. // ~~ icebear love attttttt ~~
  2. #include <bits/stdc++.h>
  3. using namespace std;
  4.  
  5. typedef long long ll;
  6. typedef pair<int, int> ii;
  7. typedef pair<int, ii> iii;
  8.  
  9. template<class T>
  10.     bool minimize(T &a, const T &b) {
  11.         if (a > b) return a = b, true;
  12.         return false;
  13.     }
  14.  
  15. template<class T>
  16.     bool maximize(T &a, const T &b) {
  17.         if (a < b) return a = b, true;
  18.         return false;
  19.     }
  20.  
  21. #define FOR(i,a,b) for(int i=(a); i<=(b); ++i)
  22. #define FORR(i,a,b) for(int i=(a); i>=(b); --i)
  23. #define REP(i, n) for(int i=0; i<(n); ++i)
  24. #define RED(i, n) for(int i=(n)-1; i>=0; --i)
  25. #define MASK(i) (1LL << (i))
  26. #define mp make_pair
  27. #define pb push_back
  28. #define fi first
  29. #define se second
  30. #define all(x) x.begin(), x.end()
  31. #define task "icebearat"
  32.  
  33. const int MOD = 1e9 + 7;
  34. const int inf = 1e9 + 27092008;
  35. const ll INF = 1e18 + 27092008;
  36. const int N = 100 + 5;
  37. int k, p, dp[N][N];
  38. vector<int> digit;
  39. string L, R;
  40.  
  41. int DP(int pos, int cnt,  bool start, bool smaller) {
  42.     if (cnt > k) return 0;
  43.     if (pos < 0) return cnt <= k;
  44.     int ret = dp[pos][cnt];
  45.     if (smaller && ~ret) return ret;
  46.     ret = 0;
  47.     int limit = (smaller ? 9 : digit[pos]);
  48.     FOR(i, 0, limit) {
  49.         bool newStart = (start | (i > 0));
  50.         int newCnt = cnt + (i == p && newStart);
  51.         ret = (ret + DP(pos - 1, newCnt, newStart, smaller | (i < limit))) % MOD;
  52.     }
  53.     if (smaller) dp[pos][cnt] = ret;
  54.     return ret;
  55. }
  56.  
  57. bool check(string &x) {
  58.     int cnt = 0;
  59.     for(char c : x) if (c - '0' == p)
  60.         cnt++;
  61.     return cnt <= k;
  62. }
  63.  
  64. int f(string &x) {
  65.     digit.clear();
  66.     for(char c : x) digit.pb(c - '0');
  67.     reverse(all(digit));
  68.     return DP((int)digit.size() - 1, 0, 0, 0);
  69. }
  70.  
  71. void init(void) {
  72.     cin >> L >> R >> k >> p;
  73. }
  74.  
  75. void process(void) {
  76.     memset(dp, -1, sizeof dp);
  77.     cout << (f(R) - f(L) + check(L) + MOD) % MOD;
  78. }
  79.  
  80. int main() {
  81.     ios_base::sync_with_stdio(0);
  82.     cin.tie(0); cout.tie(0);
  83.     if (fopen(task".inp", "r")) {
  84.         freopen(task".inp", "r", stdin);
  85.         freopen(task".out", "w", stdout);
  86.     }
  87.     int tc = 1;
  88. //    cin >> tc;
  89.     while(tc--) {
  90.         init();
  91.         process();
  92.     }
  93.     return 0;
  94. }
  95.  
  96.  
Success #stdin #stdout 0.01s 5280KB
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https://ideone.com/Pf0g4Z
language:
C++ (gcc 8.3)
created:
2 days ago
visibility:
public

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