ADDED   SRM/526-U/2C.cpp
Index: SRM/526-U/2C.cpp
==================================================================
--- SRM/526-U/2C.cpp
+++ SRM/526-U/2C.cpp
@@ -0,0 +1,122 @@
+#include <iostream>
+#include <sstream>
+#include <iomanip>
+#include <vector>
+#include <string>
+#include <map>
+#include <set>
+#include <algorithm>
+#include <numeric>
+#include <iterator>
+#include <functional>
+#include <complex>
+#include <queue>
+#include <stack>
+#include <cmath>
+#include <cassert>
+#include <cstring>
+#ifdef __GNUC__
+#include <ext/hash_map>
+#define unordered_map __gnu_cxx::hash_map
+#else
+#include <unordered_map>
+#endif
+using namespace std;
+typedef long long LL;
+typedef complex<double> CMP;
+
+class SumOfLuckiness { public:
+	long long theSum(int A, int B)
+	{
+		return theSum(B) - theSum(A-1);
+	}
+
+	LL theSum(LL X)
+	{
+		string S; {stringstream ss; ss<<X; ss>>S;}
+		memo.clear();
+		return rec(S, 0, 0);
+	}
+
+	LL rec(const string& S, int i, int dif)
+	{
+		if( i == S.size() )
+			return abs(dif);
+
+		LL total = rec(S, i+1, dif+(S[i]=='4')-(S[i]=='7'));
+		for(char c='0'; c<S[i]; ++c)
+			total += count_all(S.size() - (i+1), dif+(c=='4')-(c=='7'));
+		return total;
+	}
+
+	map<pair<int,int>, LL> memo;
+	LL count_all(int n, int dif)
+	{
+		if( n == 0 )
+			return abs(dif);
+
+		const pair<int,int> key(n, dif);
+		if( memo.count(key) )
+			return memo[key];
+
+		LL total = 0;
+		for(char c='0'; c<='9'; ++c)
+			total += count_all(n-1, dif+(c=='4')-(c=='7'));
+		return memo[key] = total;
+	}
+};
+
+// BEGIN CUT HERE
+#include <ctime>
+double start_time; string timer()
+ { ostringstream os; os << " (" << int((clock()-start_time)/CLOCKS_PER_SEC*1000) << " msec)"; return os.str(); }
+template<typename T> ostream& operator<<(ostream& os, const vector<T>& v)
+ { os << "{ ";
+   for(typename vector<T>::const_iterator it=v.begin(); it!=v.end(); ++it)
+   os << '\"' << *it << '\"' << (it+1==v.end() ? "" : ", "); os << " }"; return os; }
+void verify_case(const long long& Expected, const long long& Received) {
+ bool ok = (Expected == Received);
+ if(ok) cerr << "PASSED" << timer() << endl;  else { cerr << "FAILED" << timer() << endl;
+ cerr << "\to: \"" << Expected << '\"' << endl << "\tx: \"" << Received << '\"' << endl; } }
+#define CASE(N) {cerr << "Test Case #" << N << "..." << flush; start_time=clock();
+#define END	 verify_case(_, SumOfLuckiness().theSum(A, B));}
+int main(){
+
+CASE(0)
+	int A = 1; 
+	int B = 10; 
+	long long _ = 2LL; 
+END
+CASE(1)
+	int A = 40; 
+	int B = 47; 
+	long long _ = 8LL; 
+END
+CASE(2)
+	int A = 58; 
+	int B = 526; 
+	long long _ = 231LL; 
+END
+CASE(3)
+	int A = 4444; 
+	int B = 7777; 
+	long long _ = 2338LL; 
+END
+CASE(4)
+	int A = 585858585; 
+	int B = 858585858; 
+	long long _ = 287481025LL; 
+END
+CASE(5)
+	int A = 1; 
+	int B = 1; 
+	long long _ = 0LL; 
+END
+CASE(6)
+	int A = 1; 
+	int B = 2000000000; 
+	long long _ = -1LL; 
+END
+
+}
+// END CUT HERE