uva 1363 - Joseph's Problem(数论)

题目链接：uva 1363 - Joseph's Problem

题目大意：给定n，k，求∑i=1n(k%i).

解题思路：参考别人的，自己想了很久，详细题解

#include <cstdio>#include <cstring>#include <cmath>#include <algorithm>using namespace std;typedef long long ll;ll solve (ll n, ll k) {    ll sum = 0;    if (n > k)        sum += (n-k) * k;    ll a = sqrt(k+0.5), b = k / a;    for (ll i = a; i > 1; i--) {        ll s = k / i;        ll e = k / (i-1);        if (s > n)            break;        if (e > n)            e = n;        sum += ( (k%(s+1) + k%e) * (e - s) / 2);    }    for (ll i = 2; i <= b && i <= n; i++)        sum += k%i;    return sum;}int main () {    ll n, k;    while (scanf("%lld%lld", &n, &k) == 2) {        printf("%lld\n", solve(n, k));    }    return 0;}