feat: add mission java solution in README and README_EN for No. 538, No. 1038 (doocs#544)

Author: 0xcaffebabe

solution/0500-0599/0538.Convert BST to Greater Tree/README.md

@@ -77,7 +77,18 @@
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+class Solution {
+    int add = 0;
+    public TreeNode convertBST(TreeNode root) {
+        if (root != null) {
+            convertBST(root.right);
+            root.val += add;
+            add = root.val;
+            convertBST(root.left);
+        }
+        return root;
+    }
+}
 ```
 
 ### **...**

solution/0500-0599/0538.Convert BST to Greater Tree/README_EN.md

@@ -108,7 +108,18 @@
 ### **Java**
 
 ```java
-
+class Solution {
+    int add = 0;
+    public TreeNode convertBST(TreeNode root) {
+        if (root != null) {
+            convertBST(root.right);
+            root.val += add;
+            add = root.val;
+            convertBST(root.left);
+        }
+        return root;
+    }
+}
 ```
 
 ### **...**

solution/1000-1099/1038.Binary Search Tree to Greater Sum Tree/README.md

@@ -77,7 +77,23 @@
 <!-- 这里可写当前语言的特殊实现逻辑 -->
 
 ```java
-
+class Solution {
+    private int max = 0;
+
+    public TreeNode bstToGst(TreeNode root) {
+        if (root == null) return new TreeNode(0);
+        int temp = bstToGst(root.right).val;
+        root.val += (temp > max ? temp : max);
+        max = root.val > max ? root.val : max;
+        if (root.left != null) {
+            int temp2 = bstToGst(root.left.right).val;
+            root.left.val += max > temp2 ? max : temp2;
+            max = max > root.left.val ? max : root.left.val;
+            bstToGst(root.left.left);
+        }
+        return root;
+    }
+}
 ```
 
 ### **...**

solution/1000-1099/1038.Binary Search Tree to Greater Sum Tree/README_EN.md

@@ -108,7 +108,23 @@
 ### **Java**
 
 ```java
-
+class Solution {
+    private int max = 0;
+
+    public TreeNode bstToGst(TreeNode root) {
+        if (root == null) return new TreeNode(0);
+        int temp = bstToGst(root.right).val;
+        root.val += (temp > max ? temp : max);
+        max = root.val > max ? root.val : max;
+        if (root.left != null) {
+            int temp2 = bstToGst(root.left.right).val;
+            root.left.val += max > temp2 ? max : temp2;
+            max = max > root.left.val ? max : root.left.val;
+            bstToGst(root.left.left);
+        }
+        return root;
+    }
+}
 ```
 
 ### **...**