• Source 
    1. #include <iostream>
    2. #include <vector>
    3. using namespace std;
    4.  
    5. int arr[15];
    6. int n;
    7. vector <long long> v;
    8. void push47 ()
    9. {
    10. 	long long s=0;
    11. 	for (int i=1; i<=n; i++)
    12. 	{
    13. 		if (i!=n)
    14. 		{
    15. 			s+=arr[i];
    16. 			s=s*10;
    17. 		}
    18. 		else s+=arr[i];
    19. 	}
    20. 	v.push_back(s);
    21. }
    22.  
    23. void sinh47 (int u)
    24. {
    25. 	if (u==n+1)
    26. 	{
    27. 		push47 ();
    28. 	}
    29. 	else
    30. 	{
    31. 		arr[u]=4;
    32. 		sinh47 (u+1);
    33. 		arr[u]=7;
    34. 		sinh47 (u+1);
    35. 	}
    36. }
    37.  
    38. int BSearch (int front, int back, int x)
    39. {
    40. 	int VT=-1;
    41. 	while (front<=back)
    42. 	{
    43. 		int mid = (front+back)/2;
    44. 		if (v[mid]>=x)
    45. 		{
    46. 			VT=mid;
    47. 			back=mid-1;
    48. 		}
    49. 		else front=mid+1;
    50. 	}
    51. 	return VT;
    52. }
    53.  
    54. int main ()
    55. {
    56. 	for (int i=1; i<=10; i++)
    57. 	{
    58. 		n=i;
    59. 		sinh47 (1);
    60. 	}
    61. 	long long l, r;
    62. 	cin>>l>>r;
    63. 	long long v_l = BSearch (0, v.size(), l);
    64. 	long long v_r = BSearch (0, v.size(), r);
    65. 	long long LKSUM=0;
    66. 	if (l==r)
    67. 	{
    68. 		LKSUM=v[v_l];
    69. 	}
    70. 	else if (v[v_l]==l && v[v_r]==r)
    71. 	{
    72. 		LKSUM+=v[v_l];
    73. 		for (int i=v_l+1; i<=v_r; i++)
    74. 		{
    75. 			LKSUM+=((v[i]-v[i-1])*v[i]);
    76. 		}
    77. 	}
    78. 	else if (v[v_l]==l && v[v_r]>r)
    79. 	{
    80. 		LKSUM+=v[v_l];
    81. 		for (int i=v_l+1; i<=v_r-1; i++)
    82. 		{
    83. 			LKSUM+=((v[i]-v[i-1])*v[i]);
    84. 		}
    85. 		LKSUM+=((r-v[v_r-1])*v[v_r]);
    86. 	}
    87. 	else if (v[v_l]>l && v[v_l]<=r && v[v_r]==r)
    88. 	{
    89. 		LKSUM+=((v[v_l]-l+1)*v[v_l]);
    90. 		for (int i=v_l+1; i<=v_r; i++)
    91. 		{
    92. 			LKSUM+=((v[i]-v[i-1])*v[i]);
    93. 		}
    94. 	}
    95. 	else if (v[v_l]>l && v[v_l]<=r && v[v_r]>r)
    96. 	{
    97. 		LKSUM+=((v[v_l]-l+1)*v[v_l]);
    98. 		for (int i=v_l+1; i<=v_r-1; i++)
    99. 		{
    100. 			LKSUM+=((v[i]-v[i-1])*v[i]);
    101. 		}
    102. 		LKSUM+=((r-v[v_r-1])*v[v_r]);
    103. 	}
    104. 	else if (v[v_l]>r)
    105. 	{
    106. 		LKSUM+=((r-l+1)*v[v_l]);
    107. 	}
    108. 	cout<<LKSUM;
    109. 	return 0;
    110. }