Fix Minkowskisum

codes/Geometry/MinkowskiSum.cpp

@@ -1,15 +1,15 @@
-// A, B are convex hull rotate to min by (X, Y)
+// A, B are strict convex hull rotate to min by (X, Y)
 vector<P> Minkowski(vector<P> A, vector<P> B) {
-  vector<P> C(1, A[0] + B[0]), s1, s2;
   const int N = (int)A.size(), M = (int)B.size();
-  for(int i = 0; i < N; ++i)
-    s1.pb(A[(i + 1) % N] - A[i]);
-  for(int i = 0; i < M; i++)
-    s2.pb(B[(i + 1) % M] - B[i]);
-  for(int i = 0, j = 0; i < N || j < M;)
-    if (j >= N || (i < M && cross(s1[i], s2[j]) >= 0))
-      C.pb(C.back() + s1[i++]);
-    else
-      C.pb(C.back() + s2[j++]);
-  return hull(C), C;
+  vector<P> sa(N), sb(M), C(N + M + 1);
+  for (int i = 0; i < N; i++) sa[i] = A[(i+1)%N]-A[i];
+  for (int i = 0; i < M; i++) sb[i] = B[(i+1)%M]-B[i];
+  C[0] = A[0] + B[0];
+  for (int i = 0, j = 0; i < N || j < M; ) {
+    P e = (j>=M || (i<N && cross(sa[i], sb[j])>=0))
+      ? sa[i++] : sb[j++];
+    C[i + j] = e;
+  }
+  partial_sum(all(C), C.begin()); C.pop_back();
+  return convex_hull(C); // just to remove colinear
 }