solves bst to greater tree

Author: anishLearnsToCode

README.md

@@ -141,7 +141,7 @@
 | 521 | [Longest Uncommon Subsequence I](https://leetcode.com/problems/longest-uncommon-subsequence-i) | Easy | [![Java](assets/java.png)](src/LongestUncommonSubsequenceI.java) [![Python](assets/python.png)](python/longest_uncommon_subsequence_I.py) |
 | 530 | [Minimum Absolute Difference in BST](https://leetcode.com/problems/minimum-absolute-difference-in-bst) | Easy | [![Java](assets/java.png)](src/MinimumAbsoluteDifferenceInBST.java) [![Python](assets/python.png)](python/minimum_absolute_difference_in_bst.py) |
 | 532 | [K - Diff Pairs in Array](https://leetcode.com/problems/k-diff-pairs-in-an-array) | Easy | [![Java](assets/java.png)](src/KDiffPairsInAnArray.java) [![Python](assets/python.png)](python/k_dif_pairs_in_an_array.py) |
-| 538 | [Convert BST to Greater Tree](https://leetcode.com/problems/convert-bst-to-greater-tree) | Easy | |
+| 538 | [Convert BST to Greater Tree](https://leetcode.com/problems/convert-bst-to-greater-tree) | Easy | [![Java](assets/java.png)](src/ConvertBSTToGreaterTree.java) [![Python](assets/python.png)](python/convert_bst_to_greater_tree.py) |
 | 541 | [Reverse String II](https://leetcode.com/problems/reverse-string-ii) | Easy | |
 | 543 | [Diameter of Binary Tree](https://leetcode.com/problems/diameter-of-binary-tree) | Easy | |
 | 551 | [Student Attendance Record I](https://leetcode.com/problems/student-attendance-record-i) | Easy | |

python/convert_bst_to_greater_tree.py

@@ -0,0 +1,22 @@
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
+
+
+class Solution:
+    def __init__(self):
+        self.value = 0
+
+    def computeGreaterTree(self, root: TreeNode):
+        if root is None: return
+        self.computeGreaterTree(root.right)
+        root.val += self.value
+        self.value = root.val
+        self.computeGreaterTree(root.left)
+
+    def convertBST(self, root: TreeNode) -> TreeNode:
+        self.computeGreaterTree(root)
+        return root

src/ConvertBSTToGreaterTree.java

@@ -0,0 +1,15 @@
+public class ConvertBSTToGreaterTree {
+    int value = 0;
+
+    public TreeNode convertBST(TreeNode root) {
+        computeGreaterTree(root);
+        return root;
+    }
+
+    private void computeGreaterTree(TreeNode root) {
+        if (root == null) return;
+        computeGreaterTree(root.right);
+        root.val += value;
+        computeGreaterTree(root.left);
+    }
+}