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587.cpp
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587.cpp
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class Solution {
public:
static bool compare(vector<int>& p1, vector<int>& p2) {
if (p1[0] == p2[0]) return p1[1] < p2[1];
return p1[0] < p2[0];
}
int cross(vector<int> o, vector<int> p1, vector<int> p2) {
// OP1 x OP2
return (p1[0] - o[0]) * (p2[1] - o[1]) - (p1[1] - o[1]) * (p2[0] - o[0]);
}
vector<vector<int>> outerTrees(vector<vector<int>>& trees) {
sort(trees.begin(), trees.end(), compare);
vector<vector<int>> upper;
vector<vector<int>> lower;
int n = trees.size();
for (int i = 0; i < n; ++i) {
while (lower.size() >= 2 && cross(lower[lower.size() - 2], lower[lower.size() - 1], trees[i]) < 0) lower.pop_back();
lower.push_back(trees[i]);
}
for (int i = n - 1; i >= 0; --i) {
while (upper.size() >= 2 && cross(upper[upper.size() - 2], upper[upper.size() - 1], trees[i]) < 0) upper.pop_back();
upper.push_back(trees[i]);
}
for (auto point : upper) {
lower.push_back(point);
}
sort(lower.begin(), lower.end(), compare);
vector<vector<int>> res;
int m = lower.size();
for (int i = 0; i < m; ++i) {
if (i == 0) res.push_back(lower[i]);
else {
if ((lower[i][0] == lower[i - 1][0]) && (lower[i][1] == lower[i - 1][1])) continue;
res.push_back(lower[i]);
}
}
return res;
}
};