From ad2515ee45836792251aa079c45157aca4b628a8 Mon Sep 17 00:00:00 2001
From: Lam Haoyin <root@eatswap.org>
Date: Tue, 22 Mar 2022 00:50:34 +0800
Subject: [PATCH] add: 220321-CN [cpp]

---
 cpp/2203/220321-CN.cpp  | 36 ++++++++++++++++++++++++++++++++++++
 cpp/2203/CMakeLists.txt |  2 +-
 2 files changed, 37 insertions(+), 1 deletion(-)
 create mode 100644 cpp/2203/220321-CN.cpp

diff --git a/cpp/2203/220321-CN.cpp b/cpp/2203/220321-CN.cpp
new file mode 100644
index 0000000..3165fd9
--- /dev/null
+++ b/cpp/2203/220321-CN.cpp
@@ -0,0 +1,36 @@
+#include <functional>
+#include <unordered_set>
+
+/**
+ * Definition for a binary tree node.
+ */
+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) {}
+};
+
+/**
+ * 653. Two Sum IV - Input is a BST
+ * Given the root of a Binary Search Tree and a target number k, return true if there exist two elements in the BST such that their sum is equal to the given target.
+ */
+
+class Solution {
+public:
+	static bool findTarget(const TreeNode* root, int k) {
+		if (!root) return false;
+		std::unordered_multiset<int> s;
+		std::function<void(const TreeNode*)> traverse = [&](const TreeNode* ptr) {
+			s.insert(ptr->val);
+			if (ptr->left) traverse(ptr->left);
+			if (ptr->right) traverse(ptr->right);
+		};
+		traverse(root);
+		for (int i : s)
+			if (s.count(k - i) > (((i * 2) == k) ? 1 : 0))
+				return true;
+		return false;
+	}
+};
diff --git a/cpp/2203/CMakeLists.txt b/cpp/2203/CMakeLists.txt
index f8b6e44..bc7c4a4 100644
--- a/cpp/2203/CMakeLists.txt
+++ b/cpp/2203/CMakeLists.txt
@@ -3,4 +3,4 @@ PROJECT(2203)
 
 SET(CMAKE_CXX_STANDARD 23)
 
-ADD_EXECUTABLE(2203 220321.cpp)
+ADD_EXECUTABLE(2203 220321-CN.cpp)