add: 220418 [cpp]

cpp/2204/220418.cpp

@@ -0,0 +1,40 @@
+#include <functional>
+#include <queue>
+#include <vector>
+#include <algorithm>
+
+struct TreeNode {
+	int val;
+	TreeNode* left;
+	TreeNode* right;
+
+	explicit TreeNode(int x = 0, TreeNode* l = nullptr, TreeNode* r = nullptr) : val(x), left(l), right(r) {}
+};
+
+class Solution {
+private:
+	static int priorityQueue(TreeNode* root, int k) {
+		std::vector<int> val;
+		std::function<void(TreeNode*)> f = [&](TreeNode* ptr) {
+			if (!ptr) return;
+			val.push_back(ptr->val);
+			if (ptr->left) f(ptr->left);
+			if (ptr->right) f(ptr->right);
+		};
+
+		// O(n）
+		f(root);
+
+		// O(n)
+		std::priority_queue<int, std::vector<int>, std::greater<>> q(val.begin(), val.end());
+
+		// O(k * log(n))
+		for (int i = 1; i < k; ++i)
+			q.pop();
+		return q.top();
+	}
+public:
+	static int kthSmallest(TreeNode* root, int k) {
+		return priorityQueue(root, k);
+	}
+};

cpp/2204/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2204)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2204 220418-CN.cpp)
+ADD_EXECUTABLE(2204 220418.cpp)