P1403 [AHOI2005]约数研究

Posted 2021-12-20 misuchii

很简单的数学题啦 推一下就知道f(i) = n / i啦

AC代码：

 1 #include<bits/stdc++.h>
 2 #define pi acos(-1)
 3 typedef long long ll;
 4 typedef unsigned long long ull;
 5 using namespace std;
 6 
 7 namespace io 
 8     const int SIZE = 1e7 + 10;
 9     char inbuff[SIZE];
10     char *l, *r;
11     inline void init() 
12         l = inbuff;
13         r = inbuff + fread(inbuff, 1, SIZE, stdin);
14     
15     inline char gc() 
16         if (l == r) init();
17         return (l != r) ? *(l++) : EOF;
18     
19     void read(int &x) 
20         x = 0; char ch = gc();
21         while(!isdigit(ch)) ch = gc();
22         while(isdigit(ch)) x = x * 10 + ch - ‘0‘, ch = gc();
23     
24  using io::read;
25 
26 bool cmp(const int &a, const int &b)
27     return a > b;
28 
29 
30 int main()
31     ios::sync_with_stdio(false);
32     int n;
33     cin>>n;
34     int ans = 0;
35     for (int i = 1; i <= n; i++) ans += n / i;
36     cout<<ans<<endl;
37     return 0;
38