Someone knows good resources for convolution?

Can anyone explain how to solve D(The one that involved Geometry)?Link to the Problem

Can someone provide a test in which this solution fails for D? I've had a really tough time figuring it out (passed 10/18). Thanks.

#include <bits/stdc++.h>
using namespace std;

int main() {
	int n; cin >> n;
	long double ang = (n - 2) * 90.0 / n;
	ang = ang / 360.0 * 2 * M_PI;
	int x, y, xx, yy;
	cin >> x >> y >> xx >> yy;
	long double len = sqrt((xx - x) * (xx - x) + (yy - y) * (yy - y));
	long double xr = cos(ang) * len;
	long double yr = sin(ang) * len;
	long double ang2 = acos((xx - x) / len);
	ang2 = (ang2 - ang);
	cout << setprecision(12) << fixed;
	cout << (cos(ang2) * xr) + x << ' ';
	cout << (sin(ang2) * xr) + y << '\n';
	return 0;
}

How to solve E ?

Can anyone help me out why my code is Failing for Problem C — ORXOR

ll n;
ll arr[25];
ll count(ll i, ll ans, ll store)
{
    if(i>n) return ans^store;
    return min(count(i+1,ans,store|arr[i]),count(i+1,ans^arr[i],0));
}
void solve()
{
    cin>>n;
    for(int i=1; i<=n; ++i) cin>>arr[i];
    cout<<count(1,0,0);
}

I simply recurse over all possible combinations taking the minimum, i.e at every index i, We have two possibilities either include it in sequence or partition and start a new sequence from here.

Thanks a Lot !!

E was a cute task.

Can anyone explain the idea of "build new graph" in problem F?Thanks in advance

How to do problem F? My solution which is quite a mess because maybe I don't understand properly how to construct the graph? I used a map to assign node numbers to the pairs so that its easier to construct the adjacency list. Can someone help me?I am really stuck now :( UPD: IGNORE!! It was a stupid mistake