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  1. #include<bits/stdc++.h>
  2. using namespace std;
  3. using ll = long long;
  4. const int MOD = 1e9+7;
  5. ll power(ll x,int y){
  6. 	if(y == 0)
  7. 		return 1;
  8. 	ll res = 1;
  9. 	while(y){
  10. 		if(y&1)
  11. 			res = (res*x)%MOD;
  12. 		x = (x*x)%MOD;
  13. 		y /= 2;
  14. 	}
  15. 	return res;
  16. }
  17. int main()
  18. {
  19. 	ios_base::sync_with_stdio(0);
  20. 	cin.tie(0);
  21. 	string s;
  22. 	cin >> s;
  23. 	int n = s.length();
  24. 	ll ans = 0;
  25. 	for(int i = 0; i < n;++i){
  26. 		ll digit = s[i] - '0';
  27. 		ll num_left = i;
  28. 		ll num_right = n-i-1;
  29. 		ll left_contribution =	(num_left*(num_left+1))/2LL;
  30. 		left_contribution %= MOD;
  31. 		left_contribution = (left_contribution * digit)%MOD * power(10LL,n-i-1);
  32. 		left_contribution %= MOD;
  33. 		ll right_contribution = (power(10LL,num_right) * (9LL * num_right - 1) + 1) * digit;
  34. 		right_contribution /= 81LL;
  35. 		right_contribution %=MOD;
  36. 		ans = (ans + right_contribution + left_contribution)%MOD;
  37. 	}
  38. 	cout << ans << "\n";
  39. }
  40.  
Success #stdin #stdout 0s 4500KB
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stdin
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100500100500
stdout
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650324207
https://ideone.com/08Q1et
language:
C++14 (clang 8.0)
created:
3 years ago
visibility:
public

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