HullDiameter

Returns the two points with max distance on a convex hull (ccw, no duplicate/collinear points).

Time: O(n) 12 lines stress-tested, tested on kattis:roberthood

Needs: "Point.h"

content/geometry/HullDiameter.h — Oleksandr Bacherikov, chilli, source: https://codeforces.com/blog/entry/48868

typedef Point<ll> P;
array<P, 2> hullDiameter(vector<P> S) {
	int n = sz(S), j = n < 2 ? 0 : 1;
	pair<ll, array<P, 2>> res({0, {S[0], S[0]}});
	rep(i,0,j)
		for (;; j = (j + 1) % n) {
			res = max(res, {(S[i] - S[j]).dist2(), {S[i], S[j]}});
			if ((S[(j + 1) % n] - S[j]).cross(S[i + 1] - S[i]) >= 0)
				break;
		}
	return res.second;
}