Today I have done leetcode's November LeetCoding Challenge with cpp.

November LeetCoding Challenge 19

Description

Erect the Fence

You are given an array trees where trees[i] = [xi, yi] represents the location of a tree in the garden.

You are asked to fence the entire garden using the minimum length of rope as it is expensive. The garden is well fenced only if all the trees are enclosed.

Return the coordinates of trees that are exactly located on the fence perimeter.

Example 1:

Input: points = [[1,1],[2,2],[2,0],[2,4],[3,3],[4,2]]
Output: [[1,1],[2,0],[3,3],[2,4],[4,2]]

Example 2:

Input: points = [[1,2],[2,2],[4,2]]
Output: [[4,2],[2,2],[1,2]]

Constraints:

• 1 <= points.length <= 3000
• points[i].length == 2
• 0 <= xi, yi <= 100
• All the given points are unique.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
struct Vector {
  int x;
  int y;

  Vector(int x = 0, int y = 0) : x(x), y(y) {}
  Vector(const vector<int> &v) : x(v[0]), y(v[1]) { }

  friend ostream& operator<<(ostream &os, const Vector &v) {
    os << '(' << v.x << ',' << v.y << ')';
    return os;
  }
  bool operator<(const Vector& v) const {
    return this->x < v.x || (this->x == v.x && this->y < v.y);
  }
  Vector operator+(const Vector& v) const {
    return Vector(this->x + v.x, this->y + v.y);
  }
  Vector operator-(const Vector& v) const {
    return Vector(this->x - v.x, this->y - v.y);
  }
};

int cross(const Vector& a, const Vector& b) {
  return a.x * b.y - b.x * a.y;
}
int dot(const Vector& a, const Vector& b) {
  return a.x * b.x + a.y * b.y;
}
class Solution {
public:
  vector<vector<int>> outerTrees(vector<vector<int>>& treesVector) {
    vector<Vector> trees;
    for(const auto &tree : treesVector) {
      trees.push_back(Vector(tree));
    }
    sort(trees.begin(), trees.end());
    int len = trees.size();
    int size = 1;
    vector<int> st{0};
    for(int i = 1; i < len; ++i) {
      while(size > 1 && cross(trees[st[size - 1]] - trees[st[size - 2]], trees[i] - trees[st[size - 1]]) < 0) {
        st.pop_back();
        size -= 1;
      }
      st.push_back(i);
      size += 1;
    }
    int tmp = size;
    for(int i = len - 2; i >= 0; --i) {
      while(size > tmp && cross(trees[st[size - 1]] - trees[st[size - 2]], trees[i] - trees[st[size - 1]]) < 0) {
        st.pop_back();
        size -= 1;
      }
      st.push_back(i);
      size += 1;
    }
    sort(st.begin(), st.end());
    st.resize(unique(st.begin(), st.end()) - st.begin());
    vector<vector<int>> answer;
    for(auto i : st) {
      answer.push_back({trees[i].x, trees[i].y});
    }
    return answer;
  }
};

// Accepted
// 88/88 cases passed (91 ms)
// Your runtime beats 72.8 % of cpp submissions
// Your memory usage beats 69.6 % of cpp submissions (20.7 MB)