fd

Author: dingjikerbo

README.md

@@ -375,6 +375,7 @@
 |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||
 |560|[Subarray Sum Equals K](https://leetcode.com/problems/subarray-sum-equals-k/)| [Java](leetcode/solution/src/SubarraySumEqualsK.java)|70||
+|606|[Construct String from Binary Tree](https://leetcode.com/problems/construct-string-from-binary-tree/)|[Java](leetcode/solution/src/ConstructStringFromBinaryTree.java)|90||
 |617|[Merge Two Binary Trees](https://leetcode.com/problems/merge-two-binary-trees/)|[Java](leetcode/solution/src/MergeTwoBinaryTrees.java)|100|很简单|
 |637|[Average of Levels in Binary Tree](https://leetcode.com/problems/average-of-levels-in-binary-tree/#/description)| [Java](leetcode/solution/src/AverageOfLevelsInBinaryTree.java)|100||
 |652|[Find Duplicate Subtrees](https://leetcode.com/problems/find-duplicate-subtrees/)| [Java](leetcode/solution/src/FindDuplicateSubtrees.java)|70|开始还没思路|

leetcode/solution/src/ConstructStringFromBinaryTree.java

@@ -0,0 +1,21 @@
+/**
+ * https://leetcode.com/articles/construct-string-from-binary-tree/
+ */
+public class ConstructStringFromBinaryTree {
+
+    /**
+     * 左子树如果为空'()'是不能省略的
+     * 右子树如果为空可以省略
+     */
+    public String tree2str(TreeNode t) {
+        if (t == null) {
+            return "";
+        }
+        if (t.left == null && t.right == null) {
+            return t.val + "";
+        }
+        String left = "(" + tree2str(t.left) + ")";
+        String right = t.right != null ? "(" + tree2str(t.right) + ")" : "";
+        return t.val + left + right;
+    }
+}

leetcode/src/Main.java

@@ -4,23 +4,16 @@
 
 public class Main {
 
-    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;
-            }
+    public String tree2str(TreeNode t) {
+        if (t == null) {
+            return "";
         }
-        return root;
+        if (t.left == null && t.right == null) {
+            return t.val + "";
+        }
+        String left = "(" + tree2str(t.left) + ")";
+        String right = t.right != null ? "(" + tree2str(t.right) + ")" : "";
+        return t.val + left + right;
     }
 
     public static void main(String[] args) {