pku 2346 乘法原理

#include <iostream> #include <cmath> using namespace std; int hash[46]; int main() { int n; scanf("%d", &n); __int64 sum; for(__int64 i = 0; i < (__int64)pow(10.0, n/2); ++i) { sum = 0; __int64 p = 1; for(int j = 0; j < n/2; ++j) { sum += (i/p)%10; p *= 10; } hash[sum]++; } sum = 0; for(int i = 0; i < n/2*9+1; ++i) sum += hash[i]*hash[i]; printf("%I64d/n", sum); return 0; }