add: 220423-CN [cpp]

cpp/2204/220423-CN.cpp

@@ -0,0 +1,61 @@
+#include <algorithm>
+#include <vector>
+
+/**
+ * 587. 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.
+ *
+ * Note: it is all about computing the convex hull.
+ */
+
+class Solution {
+public:
+	static std::vector<std::vector<int>> outerTrees(std::vector<std::vector<int>>& trees) {
+		std::sort(trees.begin(), trees.end(), [](const std::vector<int>& x, const std::vector<int>& y) { return x[0] == y[0] ? x[1] < y[1] : x[0] < y[0]; });
+		int n = trees.size();
+		std::vector<std::vector<int>> top, bottom;
+
+		auto CrossProduct = [](const std::pair<int, int>& x, const std::pair<int, int>& y) {
+			// x, y are vectors
+			return x.first * y.second - x.second * y.first;
+		};
+
+		std::for_each(trees.cbegin(), trees.cend(), [&](const std::vector<int>& p) {
+			while (bottom.size() > 1 && [&](){
+				int n = bottom.size();
+				const auto& b1 = bottom[n - 1];
+				const auto& b2 = bottom[n - 2];
+				return CrossProduct({b1[0] - b2[0], b1[1] - b2[1]}, {p[0] - b1[0], p[1] - b1[1]}) < 0;
+			}()) bottom.pop_back();
+			bottom.push_back(p);
+		});
+
+		std::for_each(trees.crbegin(), trees.crend(), [&](const std::vector<int>& p) {
+			while (top.size() > 1 && [&](){
+				int n = top.size();
+				const auto& b1 = top[n - 1];
+				const auto& b2 = top[n - 2];
+				return CrossProduct({b1[0] - b2[0], b1[1] - b2[1]}, {p[0] - b1[0], p[1] - b1[1]}) < 0;
+			}()) top.pop_back();
+			top.push_back(p);
+		});
+
+		std::vector<std::vector<int>> ret;
+		bool x[65536]{};
+		for (const auto& p : top) {
+			if (x[(p[0] << 8) | p[1]])
+				continue;
+			x[(p[0] << 8) | p[1]] = true;
+			ret.push_back(p);
+		}
+		for (const auto& p : bottom) {
+			if (x[(p[0] << 8) | p[1]])
+				continue;
+			x[(p[0] << 8) | p[1]] = true;
+			ret.push_back(p);
+		}
+		return ret;
+	}
+};

cpp/2204/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2204)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2204 220424.cpp)
+ADD_EXECUTABLE(2204 220423-CN.cpp)