BZOJ2045 双亲数

2301的弱化版。。。（弱过头了的说）

真是。。。为什么2301都1A了这道题却1RE+1A啊。。。蒟蒻到底了。。。

什么时候搞懂了再写题解什么的。。。

/**************************************************************
    Problem: 2045
    User: rausen
    Language: C++
    Result: Accepted
    Time:360 ms
    Memory:9596 kb
****************************************************************/
 
#include <cstdio>
#include <cmath>
#include <algorithm>
 
using namespace std;
typedef long long ll;
const int N = 1000005;
int u[N], p[N], tot;
bool v[N];
 
inline int read(){
    int x = 0;
    char ch = getchar();
    while (ch < '0' || ch > '9')
        ch = getchar();
         
    while (ch >= '0' && ch <= '9'){
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return x;
}
 
void pre_work(){
    u[1] = 1;
    int i, j, K;
    for (i = 2; i < N; ++i){
        if (!v[i])
            p[++tot] = i, u[i] = -1;
        for (j = 1; i * p[j] < N && j <= tot; ++j){
            v[K = i * p[j]] = 1;
            if (i % p[j] == 0){
                u[K] = 0; 
                break;
            }else u[K] = -u[i];
        }
    }
    for (i = 2; i < N; ++i)
        u[i] += u[i - 1];
}
 
ll work(int n, int m, int k){
    n /= k, m /= k;
    if (n > m) swap(n, m);
    ll res = 0;
    int i, last;
    for (i = 1; i <= n; i = last + 1){
        last = min(n / (n / i), m / (m / i));
        res += (ll) (u[last] - u[i - 1]) * (n / i) * (m / i);
    }
    return res;
}
 
int main(){
    pre_work();
    int a = read(), b = read(), k = read();
    printf("%lld
", work(a, b, k));
    return 0;
}