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  1. #include <bits/stdc++.h> 
  2.  
  3. using namespace std;  
  4.  
  5. typedef long long ll;  
  6. typedef pair<int, int> ii;  
  7.  
  8. const int INF = 1e9;  
  9. const ll LINF = 1e18;  
  10.  
  11. const int MOD = 1e9 + 7; 
  12. const int N = 5e5 + 5; 
  13.  
  14. void add(int& a, int b) {
  15. 	a += b; 
  16. 	if (a >= MOD) a -= MOD; 
  17. }
  18.  
  19. int n; 
  20. string s; 
  21.  
  22. int nxt[N][26]; // nxt[i][c] = Vị trí i' gần nhất > i sao cho s[i'] = c 
  23.  
  24. void precompute() {
  25. 	for (int c = 0; c <= 25; c++) nxt[n][c] = n + 1; 
  26.  
  27. 	for (int i = n - 1; i >= 0; i--) {
  28. 		for (int c = 0; c <= 25; c++) nxt[i][c] = nxt[i + 1][c];
  29. 		nxt[i][s[i + 1] - 'a'] = i + 1; 
  30. 	}
  31. }
  32.  
  33. int dp[N]; // dp[i] = Số xâu con phân biệt kết thúc tại vị trí i
  34.  
  35. int main() {
  36. 	ios::sync_with_stdio(false); 
  37. 	cin.tie(nullptr); 	
  38. 	cin >> s; 
  39. 	n = s.size();  
  40. 	s = ' ' + s;  
  41.  
  42. 	precompute();   
  43.  
  44. 	dp[0] = 1;  
  45. 	for (int i = 0; i < n; i++) {
  46. 		for (int c = 0; c <= 25; c++) {
  47. 			add(dp[nxt[i][c]], dp[i]); 
  48. 		}
  49. 	}
  50.  
  51. 	int ans = 0;  
  52. 	for (int i = 1; i <= n; i++) add(ans, dp[i]); 
  53.  
  54. 	cout << ans << '\n'; 
  55. }
Success #stdin #stdout 0.01s 5600KB
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https://ideone.com/kOTpGK
language:
C++14 (gcc 8.3)
created:
1 year ago
visibility:
secret

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