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Author: assassint2017

Binary Search Tree to Greater Sum Tree/Binary_Search_Tree_to_Greater_Sum_Tree.cpp

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+// Runtime: 4 ms, faster than 61.67% of C++ online submissions for Binary Search Tree to Greater Sum Tree.
+// Memory Usage: 9.4 MB, less than 100.00% of C++ online submissions for Binary Search Tree to Greater Sum 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:
+    TreeNode* bstToGst(TreeNode* root) 
+    {
+        vector<int> nums;
+        
+        inOrderTraversal(root, nums);
+        
+        unordered_map<int, int> hashmap;
+        int temp = 0;
+        for (int i = nums.size() - 1; i >= 0; --i)
+        {
+            temp += nums[i];
+            hashmap.insert(make_pair(nums[i], temp));
+        }
+        
+        inOrderModify(root, hashmap);
+        return root;
+    }
+private:
+    void inOrderTraversal(TreeNode* root, vector<int>& nums)
+    {
+        stack<TreeNode*> memo;
+        while (root || !memo.empty())
+        {
+            while (root)
+            {
+                memo.push(root);
+                root = root->left;
+            }
+            if (!memo.empty())
+            {
+                root = memo.top();
+                memo.pop();
+                
+                nums.push_back(root->val);
+                
+                root = root->right;
+            }
+        }
+    }
+    
+    void inOrderModify(TreeNode* root, unordered_map<int, int>& hashmap)
+    {
+        stack<TreeNode*> memo;
+        while (root || !memo.empty())
+        {
+            while (root)
+            {
+                memo.push(root);
+                root = root->left;
+            }
+            if (!memo.empty())
+            {
+                root = memo.top();
+                memo.pop();
+                
+                root->val = hashmap.at(root->val);
+                
+                root = root->right;
+            }
+        }
+    }
+};