Add files via upload

Author: assassint2017

Diameter of Binary Tree/Diameter_of_Binary_Tree.cpp

@@ -0,0 +1,84 @@
+// 第一种方案，使用简单递归进行处理，虽然过了，但是明显很慢，加入备忘录之后提升也不是很明显
+
+// Runtime: 56 ms, faster than 8.09% of C++ online submissions for Diameter of Binary Tree.
+// Memory Usage: 35.5 MB, less than 7.41% of C++ online submissions for Diameter of Binary Tree.
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution 
+{
+public:
+    int diameterOfBinaryTree(TreeNode* root) 
+    {
+        if (root == nullptr)
+            return 0;
+        
+        int a = getDepth(root->left) + getDepth(root->right);
+        int b = diameterOfBinaryTree(root->left);
+        int c = diameterOfBinaryTree(root->right);
+        
+        return max(a, max(b, c));
+    }
+private:
+    unordered_map<TreeNode*, int> hashmap;
+
+    int getDepth(TreeNode* root)
+    {
+        if (root == nullptr)
+            return 0;
+        
+        if (hashmap.find(root) == hashmap.end())
+        {
+            int left = getDepth(root->left);
+            int right = getDepth(root->right);
+
+            hashmap.insert(root, max(left, right) + 1);
+        }
+        return hashmap.at(root);
+    }
+};
+
+// 第2种方案，速度提升还是非常明显的
+// Runtime: 12 ms, faster than 68.92% of C++ online submissions for Diameter of Binary Tree.
+// Memory Usage: 19.6 MB, less than 92.59% of C++ online submissions for Diameter of Binary Tree.
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+class Solution 
+{
+public:
+    int diameterOfBinaryTree(TreeNode* root) 
+    {
+        getDepth(root);
+        return res;
+    }
+private:
+    int res = 0;
+
+    int getDepth(TreeNode* root)
+    {
+        if (root == nullptr)
+            return 0;
+        
+        int left = getDepth(root->left);
+        int right = getDepth(root->right);
+
+        res = max(res, left + right);
+
+        return max(left, right) + 1;
+    }
+};