Fix min enclosing circle and add tested comment

codes/Geometry/Circle/MinCircleCover.cpp

@@ -1,25 +1,25 @@
-// be careful of type
-Cir getCircum(P a, P b, P c){
+Cir getCircum(P a, P b, P c){ // P = complex<llf>
   P z1 = a - b, z2 = a - c; llf D = cross(z1, z2) * 2;
   llf c1 = dot(a + b, z1), c2 = dot(a + c, z2);
-  P o = (c2 * conj(z1) - c1 * conj(z2)) / D;
+  P o = rot90(c2 * z1 - c1 * z2) / D;
   return { o, abs(o - a) };
 }
 Cir minCircleCover(vector<P> &pts) {
-  shuffle(pts.begin(), pts.end(), mt19937(114514));
-  Cir c = { pts[0], 0 };
-  for(int i = 0; i < (int)pts.size(); i++) {
+  assert (!pts.empty());
+  ranges::shuffle(pts, mt19937(114514));
+  Cir c = { 0, 0 };
+  for(size_t i = 0; i < pts.size(); i++) {
     if (dist(pts[i], c.o) <= c.r) continue;
     c = { pts[i], 0 };
-    for (int j = 0; j < i; j++) {
+    for (size_t j = 0; j < i; j++) {
       if (dist(pts[j], c.o) <= c.r) continue;
       c.o = (pts[i] + pts[j]) / llf(2);
       c.r = dist(pts[i], c.o);
-      for (int k = 0; k < j; k++) {
+      for (size_t k = 0; k < j; k++) {
         if (dist(pts[k], c.o) <= c.r) continue;
         c = getCircum(pts[i], pts[j], pts[k]);
       }
     }
   }
   return c;
-}
+} // test @ TIOJ 1093 & luogu P1742