add 226

Author: shishishu

README.md

@@ -34,4 +34,5 @@ Idx | Date | Question | Python| Java | Domain | Tag | Difficulty | Remark
 028|20200301|[450. Delete Node in a BST](https://leetcode.com/problems/delete-node-in-a-bst/)|[450p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/450_Delete_Node_in_a_BST.ipynb)|[450j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/450/Solution.java)|BST|Recursive|Medium
 029|20200329|[538. Convert BST to Greater Tree](https://leetcode.com/problems/convert-bst-to-greater-tree/)|[538p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/538_Convert_BST_to_Greater_Tree.ipynb)|[538j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/538/Solution.java)|BST|Recursive/Iterative|Easy
 030|20200329|[1. Two Sum](https://leetcode.com/problems/two-sum/)|[001p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/001_Two_Sum.ipynb)|[001j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/001/Solution.java)|Array|HashTable|Easy
-031|20200329|[653. Two Sum IV - Input is a BST](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/)|[653p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/653_Two_Sum_IV_-_Input_is_a_BST.ipynb)|[653j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/653/Solution.java)|BST| |Easy
+031|20200329|[653. Two Sum IV - Input is a BST](https://leetcode.com/problems/two-sum-iv-input-is-a-bst/)|[653p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/653_Two_Sum_IV_-_Input_is_a_BST.ipynb)|[653j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/653/Solution.java)|BST| |Easy
+032|20200406|[226. Invert Binary Tree](https://leetcode.com/problems/invert-binary-tree/)|[226p](https://github.com/shishishu/leetcode-python-java/blob/master/ipynb_files/226_Invert_Binary_Tree.ipynb)|[226j](https://github.com/shishishu/leetcode-python-java/blob/master/java_codes/226/Solution.java)|Tree|Recursive/Iterative|Easy

images/226_Q.PNG

@@ -0,0 +1,42 @@
+import java.util.Stack;
+
+class TreeNode {
+    int val;
+    TreeNode left;
+    TreeNode right;
+    TreeNode(int x) {
+        val = x;
+    }
+}
+
+// Recursive
+class Solution {
+    public TreeNode invertTree(TreeNode root) {
+        if (root != null){
+            TreeNode rightNode = invertTree(root.right);
+            TreeNode leftNode = invertTree(root.left);
+            root.right = leftNode;
+            root.left = rightNode;
+        }
+        return root;
+    }
+}
+
+// Iterative
+class Solution {
+    public TreeNode invertTree(TreeNode root) {
+        Stack<TreeNode> stack = new Stack<>();
+        stack.add(root);
+        while (!stack.isEmpty()){
+            TreeNode curr = stack.pop();
+            if (curr != null){
+                TreeNode tmp = curr.right;
+                curr.right = curr.left;
+                curr.left = tmp;
+                stack.add(curr.left);
+                stack.add(curr.right);
+            }
+        }
+        return root;
+    }
+}

images/226_S1.PNG

@@ -35,6 +35,7 @@
       <sourceFolder url="file://$MODULE_DIR$/538" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/001" isTestSource="false" />
       <sourceFolder url="file://$MODULE_DIR$/653" isTestSource="false" />
+      <sourceFolder url="file://$MODULE_DIR$/226" isTestSource="false" />
     </content>
     <orderEntry type="inheritedJdk" />
     <orderEntry type="sourceFolder" forTests="false" />