add: 230311

cpp/2303/230311.cpp

@@ -0,0 +1,98 @@
+#include <vector>
+#include <algorithm>
+#include <cstdio>
+#include <string>
+
+struct TreeNode {
+	int val;
+	TreeNode* left;
+	TreeNode* right;
+
+	explicit TreeNode(int x = 0, TreeNode* left = nullptr, TreeNode* right = nullptr) : val(x), left(left), right(right) {}
+};
+
+struct ListNode {
+	int val;
+	ListNode* next;
+
+	explicit ListNode(int x = 0, ListNode* next = nullptr) : val(x), next(next) {}
+};
+
+ListNode* construct(int x) {
+	return new ListNode(x);
+}
+
+template<typename... Ts>
+ListNode* construct(int x, Ts... xs) {
+	return new ListNode(x, construct(xs...));
+}
+
+/**
+ * 109. Convert Sorted List to Binary Search Tree
+ *
+ * Given the head of a singly linked list where elements are sorted in ascending order, convert it to a height-balanced binary search tree.
+ */
+
+class Solution {
+private:
+	static TreeNode* helper(const std::vector<int>& v, int s, int e) {
+		switch (e - s) {
+			case 1:
+				return new TreeNode(v[s]);
+			case 2:
+				return new TreeNode(v[s + 1], new TreeNode(v[s]), nullptr);
+		}
+		int mid = (s + e) >> 1;
+		return new TreeNode(
+			v[mid],
+			helper(v, s, mid),
+			helper(v, mid + 1, e)
+		);
+	}
+
+public:
+	static TreeNode* sortedListToBST(ListNode* head) {
+		if (!head)
+			return nullptr;
+		std::vector<int> v;
+		for (const ListNode* ptr = head; ptr; ptr = ptr->next)
+			v.push_back(ptr->val);
+		return helper(v, 0, v.size());
+	}
+};
+
+int h(const TreeNode* r) {
+	return r ? std::max(h(r->left), h(r->right)) + 1 : 0;
+}
+
+bool isBalanced(const TreeNode* r) {
+	if (!r)
+		return true;
+	if (!isBalanced(r->left)) {
+		std::printf("Not balanced: val = %d, L not balanced.\n", r->val);
+		return false;
+	} else if (!isBalanced(r->right)) {
+		std::printf("Not balanced: val = %d, R not balanced.\n", r->val);
+		return false;
+	}
+	int hl = h(r->left), hr = h(r->right);
+	if (std::abs(hl - hr) > 1) {
+		std::printf("Not balanced, val = %d, hl = %d, hr = %d\n", r->val, hl, hr);
+		return false;
+	}
+	return true;
+}
+
+std::string to_string(const TreeNode* r) {
+	if (!r)
+		return "[]";
+	return std::string("[") + std::to_string(r->val) + to_string(r->left) + to_string(r->right) + "]";
+}
+
+int main() {
+	ListNode* h = construct(-10, -3, 0, 5, 9, 10, 12, 14, 666, 3344);
+	TreeNode* r = Solution::sortedListToBST(h);
+	std::printf("%s\n", to_string(r).c_str());
+	std::printf("Is balanced: %s\n", isBalanced(r) ? "true" : "false");
+	return 0;
+}

cpp/2303/CMakeLists.txt

@@ -3,4 +3,4 @@ PROJECT(2303)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2303 230310.cpp)
+ADD_EXECUTABLE(2303 230311.cpp)