2 Closest Points in 2D Plane (N log^2 N).cpp

struct Point
{
	int x, y;

	Point operator -(Point p)
	{
		return {x-p.x, y-p.y};
	}

	int dist()
	{
		return x*x + y*y;
	}
};

bool by_x(Point &a, Point &b)
{
	return a.x < b.x;
}

bool by_y(Point &a, Point &b)
{
	return a.y < b.y;
}

int n, ans=1e18;
int a[N], pref[N];
Point pt[N];

int solve(int L, int R)
{
	if(L==R)
		return 1e18;
	int M=(L+R)/2;
	sort(pt+L, pt+R+1, by_x);
	int d=min(solve(L, M), solve(M+1, R));
	int midx=pt[L+(R-L+1)/2].x;
	vector<Point> v;
	for(int i=L;i<=R;i++)
	{
		if(Point{pt[i].x-midx, 0}.dist()<d)
		{
			v.push_back(pt[i]);
		}
	}
	sort(v.begin(), v.end(), by_y);
	for(int i=0;i<v.size();i++)
	{
		for(int j=i+1;j<v.size();j++)
		{
			if(Point{0, v[i].y-v[j].y}.dist()>d)
				break;
			d=min(d, (v[i]-v[j]).dist());
		}
	}
	return d;
}   

Problem 1: http://codeforces.com/contest/429/problem/D
Solution 1: http://codeforces.com/contest/429/submission/39494778