PR003004(Digit Sum) SPOJ PROBLEM SOLUTION

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HII GUYS THIS IS MY AC C++ SOLUTION if u want to know the logic behind this u can rerfer my another post for explanation http://spojdev.blogspot.in/2015/01/formula-for-calculating-sum-of-digits.html #include<iostream> #include<cstdio> #include<cmath> #define LL long long int using namespace std; LL sum(LL N) { if(N/10==0) return N*(N+1)/2; int i=0; LL n=N; while(n/10!=0){ i++; n/=10; } LL p=pow(10,i); return ((n*45*i*p/10)+ n*(n-1)*p/2+ n*(N%p+1) + sum(N%p)); } int main() { LL a,b,t; scanf("%lld",&t); while(t--) { cin>>a>>b; cout<<sum(b)-sum(a-1)<<endl; } return 0; }