add: 230219

cpp/2302/230219.cpp

@@ -0,0 +1,45 @@
+#include <vector>
+#include <utility>
+#include <queue>
+#include <algorithm>
+
+struct TreeNode {
+	int val;
+	TreeNode* left;
+	TreeNode* right;
+
+	explicit TreeNode(int x, TreeNode* left = nullptr, TreeNode* right = nullptr) : val(x), left(left), right(right) {}
+};
+
+/**
+ * 103. Binary Tree Zigzag Level Order Traversal
+ *
+ * Given the root of a binary tree, return the zigzag level order traversal of its nodes' values. (i.e., from left to right, then right to left for the next level and alternate between).
+ */
+
+class Solution {
+public:
+	static std::vector<std::vector<int>> zigzagLevelOrder(const TreeNode* root) {
+		if (!root)
+			return {};
+		std::vector<std::vector<int>> ret {{}};
+		std::queue<std::pair<const TreeNode*, int>> q;
+		q.emplace(root, 0);
+		for (int n = 0; !q.empty(); ) {
+			const auto [ptr, lv] = q.front();
+			q.pop();
+			if (lv > n) {
+				ret.emplace_back();
+				++n;
+			}
+			ret.back().push_back(ptr->val);
+			if (ptr->left)
+				q.emplace(ptr->left, 1 + lv);
+			if (ptr->right)
+				q.emplace(ptr->right, 1 + lv);
+		}
+		for (int i = 1; i < ret.size(); i += 2)
+			std::reverse(ret[i].begin(), ret[i].end());
+		return ret;
+	}
+};

cpp/CMakeLists.txt

@@ -16,7 +16,7 @@ ENDIF()
 # Optimisation
 # SET(CMAKE_CXX_FLAGS "${CMAKE_CXX_FLAGS} -Ofast -march=native -mtune=native -finline-functions -ffast-math -fomit-frame-pointer")
 
-ADD_EXECUTABLE(leetcode-cpp main.cpp 2302/230218.cpp 2302/230218-CN.cpp 2302/230219-CN.cpp)
+ADD_EXECUTABLE(leetcode-cpp main.cpp 2302/230218.cpp 2302/230218-CN.cpp 2302/230219-CN.cpp 2302/230219.cpp)
 
 # ADD_SUBDIRECTORY(2112)
 # ADD_SUBDIRECTORY(2201)