question:
$$sum_{i=1}^{n} k mod i$$
$$sum_{i=1}^{n} k - lfloor frac{k}{i}
floor i$$
$$sum_{i=1}^{n}k - sum_{i=1}^{n}lfloor frac{k}{i}
floor i$$
直接数论分块
#include <iostream> int main() { int n, k; long long Answer = 0; std:: cin >> n >> k; for(int i = 1, r; i <= n; i = r + 1) { if(k / i) r = std:: min(n, (int)k / (k / i)); else r = n; Answer += (1LL * (r - i + 1) * k - 1LL * (k / i) * (i + r) * (r - i + 1) / 2); } std:: cout << Answer; return 0; }