add: 230419

cpp/2304/230419.cpp

@@ -0,0 +1,58 @@
+#include <algorithm>
+#include <numeric>
+#include <unordered_map>
+#include <utility>
+
+struct TreeNode {
+	int val;
+	TreeNode* left;
+	TreeNode* right;
+
+	explicit TreeNode(int x, TreeNode* left = nullptr, TreeNode* right = nullptr) : val(x), left(left), right(right) {}
+};
+
+/**
+ * 1372. Longest ZigZag Path in a Binary Tree
+ *
+ * You are given the root of a binary tree.
+ *
+ * A ZigZag path for a binary tree is defined as follow:
+ *
+ * Choose any node in the binary tree and a direction (right or left).
+ * If the current direction is right, move to the right child of the current node; otherwise, move to the left child.
+ * Change the direction from right to left or from left to right.
+ * Repeat the second and third steps until you can't move in the tree.
+ * Zigzag length is defined as the number of nodes visited - 1. (A single node has a length of 0).
+ *
+ * Return the longest ZigZag path contained in that tree.
+ */
+
+class Solution {
+private:
+	std::pair<int, int> f(TreeNode* r) noexcept;
+
+	std::unordered_map<TreeNode*, std::pair<int, int>> m;
+
+public:
+	int longestZigZag(TreeNode* root) noexcept;
+};
+
+int Solution::longestZigZag(TreeNode* root) noexcept {
+	f(root);
+	return std::transform_reduce(m.begin(), m.end(), 0, [](int x, int y) { return std::max(x, y); }, [](auto&& x) {
+		return std::max(x.second.first, x.second.second);
+	});
+}
+
+std::pair<int, int> Solution::f(TreeNode* r) noexcept {
+	if (m.count(r))
+		return m[r];
+	return m[r] = {
+		r->left ? f(r->left).second + 1 : 0,
+		r->right ? f(r->right).first + 1 : 0
+	};
+}
+
+int main() {
+	return 0;
+}

cpp/2304/CMakeLists.txt

@@ -4,4 +4,4 @@ PROJECT(2304)
 SET(CMAKE_CXX_STANDARD 23)
 SET(CMAKE_EXPORT_COMPILE_COMMANDS true)
 
-ADD_EXECUTABLE(2304 230420-CN.cpp)
+ADD_EXECUTABLE(2304 230419.cpp)