fd

Author: dingjikerbo

README.md

@@ -370,6 +370,7 @@
 |524|[Longest Word in Dictionary through Deleting](https://leetcode.com/problems/longest-word-in-dictionary-through-deleting/)| [Java](leetcode/solution/src/LongestWordInDictionaryThroughDeleting.java)|||
 |526|[Beautiful Arrangement](https://leetcode.com/problems/beautiful-arrangement/)| [Java](leetcode/solution/src/BeautifulArrangement.java)|80||
 |535|[Encode and Decode TinyURL](https://leetcode.com/problems/encode-and-decode-tinyurl/)| [Java](leetcode/solution/src/EncodeAndDecodeTinyURL.java)|100||
+|538|[Convert BST to Greater Tree](https://leetcode.com/problems/convert-bst-to-greater-tree/)|[Java](leetcode/solution/src/ConvertBSTToGreaterTree.java)|100||
 |541|[Reverse String II](https://leetcode.com/problems/reverse-string-ii/)| [Java](leetcode/solution/src/ReverseStringII.java)|100||
 |543|[Diameter of Binary Tree](https://leetcode.com/problems/diameter-of-binary-tree/)|[Java](leetcode/solution/src/DiameterOfBinaryTree.java)|80|这题易错|
 |557|[Reverse Words in a String III](https://leetcode.com/problems/reverse-words-in-a-string-iii/)| [Java](leetcode/solution/src/ReverseWordsInAStringIII.java)|100||

leetcode/solution/src/ConvertBSTToGreaterTree.java

@@ -0,0 +1,26 @@
+import java.util.Stack;
+
+/**
+ * https://leetcode.com/articles/convert-bst-to-greater-tree/
+ */
+public class ConvertBSTToGreaterTree {
+
+    public TreeNode convertBST(TreeNode root) {
+        Stack<TreeNode> stack = new Stack<>();
+        int sum = 0;
+        TreeNode node = root;
+        while (!stack.isEmpty() || node != null) {
+            if (node != null) {
+                stack.push(node);
+                node = node.right;
+            } else {
+                node = stack.pop();
+                int s = sum;
+                sum += node.val;
+                node.val += s;
+                node = node.left;
+            }
+        }
+        return root;
+    }
+}

leetcode/src/Main.java

@@ -4,31 +4,23 @@
 
 public class Main {
 
-    public int pathSum(TreeNode root, int sum) {
-        HashMap<Integer, Integer> map = new HashMap<>();
-        map.put(0, 1);
-
-        int[] count = new int[1];
-        helper(root, sum, 0, map, count);
-        return count[0];
-    }
-
-    private void helper(TreeNode node, int target, int sum, HashMap<Integer, Integer> map, int[] count) {
-        if (node == null) {
-            return;
-        }
-
-        sum += node.val;
-        if (map.containsKey(sum - target)) {
-            count[0] += map.get(sum - target);
+    public TreeNode convertBST(TreeNode root) {
+        Stack<TreeNode> stack = new Stack<>();
+        int sum = 0;
+        TreeNode node = root;
+        while (!stack.isEmpty() || node != null) {
+            if (node != null) {
+                stack.push(node);
+                node = node.right;
+            } else {
+                node = stack.pop();
+                int s = sum;
+                sum += node.val;
+                node.val += s;
+                node = node.left;
+            }
         }
-
-        map.put(sum, map.getOrDefault(sum, 0) + 1);
-
-        helper(node.left, target, sum, map, count);
-        helper(node.right, target, sum, map, count);
-
-        map.put(sum, map.getOrDefault(sum, 0) - 1);
+        return root;
     }
 
     public static void main(String[] args) {