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Add geometry/convex_hull.cc 

Signed-off-by: subcrip <contact@subc.rip>
This commit is contained in:
subcrip 2024-11-09 18:58:46 +08:00
parent 2100b97d42
commit 367c0bef37
1 changed files with 38 additions and 0 deletions
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geometry/convex_hull.cc Normal file
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struct convex_hull {
int n, m;
vector<int> on_hull;
// WARN: counter-clockwise
vector<int> hull;
// WARN: sort the points before initializing
template <typename T>
convex_hull(const vector<point<T>>& a) : n(a.size()), on_hull(n) {
for (int i = 0; i < n; ++i) {
int m = hull.size();
// WARN: keeping the points that are on edges
while (m > 1 and (a[hull[m - 1]] - a[hull[m - 2]]) * (a[i] - a[hull[m - 2]]) < 0) {
on_hull[hull[m - 1]] -= 1;
hull.pop_back();
m -= 1;
}
on_hull[i] += 1;
hull.emplace_back(i);
}
int low = hull.size();
for (int i = n - 2; ~i; --i) {
int m = hull.size();
while (m > low and (a[hull[m - 1]] - a[hull[m - 2]]) * (a[i] - a[hull[m - 2]]) < 0) {
on_hull[hull[m - 1]] -= 1;
hull.pop_back();
m -= 1;
}
on_hull[i] += 1;
hull.emplace_back(i);
}
if (n > 1) {
hull.pop_back();
}
m = hull.size();
}
};