C. Polygon for the Angle(计算几何,数论)
C. Polygon for the Angle
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
You are given an angle angang.
The Jury asks You to find such regular nn-gon (regular polygon with nn vertices) that it has three vertices aa, bb and cc (they can be non-consecutive) with ∠abc=ang∠abc=ang or report that there is no such nn-gon.
If there are several answers, print the minimal one. It is guarantied that if answer exists then it doesn't exceed 998244353998244353.
Input
The first line contains single integer TT (1≤T≤1801≤T≤180) — the number of queries.
Each of the next TT lines contains one integer angang (1≤ang<1801≤ang<180) — the angle measured in degrees.
Output
For each query print single integer nn (3≤n≤9982443533≤n≤998244353) — minimal possible number of vertices in the regular nn-gon or −1−1 if there is no such nn.
Example
input
Copy
4
54
50
2
178
output
Copy
10
18
90
180
Note
The answer for the first query is on the picture above.
The answer for the second query is reached on a regular 1818-gon. For example, ∠v2v1v6=50∘∠v2v1v6=50∘.
The example angle for the third query is ∠v11v10v12=2∘∠v11v10v12=2∘.
In the fourth query, minimal possible nn is 180180 (not 9090).
解析:
m边形最大为(m-2)*180/m的∠
可以分出(1/(m-2))*x*[(m-2)*180/m]的∠ (1<=x<=m-2), 1~(m-2) 个 180/m 的∠合并
公式:x/m=n/180,(x,n,m都为整数)
结果为:180/gcd(180,n)
但最大∠要大于(m-2)*180/m
所以如果小于,就✖2
ac:
#include<bits/stdc++.h>
#define ll long long
using namespace std;
int gcd(int a,int b){return b==0?a:gcd(b,a%b);}
int main()
{
int t,n;
scanf("%d",&t);
while(t--)
{
scanf("%d",&n);
int x=180/gcd(180,n);
if(n>((x-2)*180/x))
cout<<x*2<<endl;
else cout<<x<<endl;
}
return 0;
}