Binary Tree Traversals - inorder, preorder, postorder java (#23)

Author: girishgr8

Java/binary-tree-inorder-traversal.java

@@ -0,0 +1,37 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ *
+ * Runtime: 0 ms
+ * Memory Usage: 37.8 MB
+ *
+ */
+
+class Solution {
+    public List<Integer> inorderTraversal(TreeNode root) {
+        List<Integer> list = new ArrayList<Integer>();
+        inorder(root, list);
+        return list;
+    }
+
+    public void inorder(TreeNode root, List<Integer> list){
+	/* Inorder traversal is visiting : left subtree then root then right subtree */
+
+	/* if node is null, then return back to the caller function */
+        if(root==null)
+            return;
+	/* Recurse for left subtree */
+        inorder(root.left, list);
+
+	/* Add the current node's value to the list */
+        list.add(root.val);
+
+	/* Recurse for right subtree */
+        inorder(root.right, list);
+    }
+}

Java/binary-tree-postorder-traversal.java

@@ -0,0 +1,37 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ *
+ * Runtime: 0 ms
+ * Memory Usage: 37.9 MB
+ *
+ */
+class Solution {
+    List<Integer> list = new ArrayList<Integer>();
+    public List<Integer> postorderTraversal(TreeNode root) {
+        postorder(root);
+        return list;
+    }
+
+    public void postorder(TreeNode root){
+	/* Postorder traversal is visiting : left subtree then right subtree then root */
+
+	/* if node is null, then return back to the caller function */
+        if(root==null)
+            return;
+	
+	/* Recurse for left subtree */
+        postorderTraversal(root.left);
+
+	/* Recurse for right subtree */
+        postorderTraversal(root.right);
+
+	/* Add the current node's value to the list */
+        list.add(root.val);
+    }
+}

Java/binary-tree-preorder-traversal.java

@@ -0,0 +1,37 @@
+/**
+ * Definition for a binary tree node.
+ * public class TreeNode {
+ *     int val;
+ *     TreeNode left;
+ *     TreeNode right;
+ *     TreeNode(int x) { val = x; }
+ * }
+ *
+ * Runtime: 0 ms
+ * Memory Usage: 37.9 MB	
+ *
+ */
+
+class Solution {
+    public List<Integer> preorderTraversal(TreeNode root) {
+        List<Integer> ls = new ArrayList<Integer>();
+        preorder(root, ls);
+        return ls;
+    }
+    public void preorder(TreeNode root, List<Integer> ls){
+	/* Preorder traversal is visiting : root then left subtree then right subtree */
+
+	/* if node is null, then return back to the caller function */
+        if(root==null)
+            return;
+
+	/* Add the current node's value to the list */
+        ls.add(root.val);
+
+	/* Recurse for left subtree */
+        preorder(root.left, ls);
+
+	/* Recurse for right subtree */
+        preorder(root.right, ls);
+    }
+}

README.md

@@ -130,11 +130,14 @@ Check out ---> [Sample PR](https://github.com/codedecks-in/LeetCode-Solutions/pu
 
 ## Tree
 
-| #   | Title                                                                                         | Solution                                                   | Time      | Space     | Difficulty | Tag                             | Note |
-| --- | --------------------------------------------------------------------------------------------- | ---------------------------------------------------------- | --------- | --------- | ---------- | ------------------------------- | ---- |
-| 103 | [ZigZag Level Order](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/) | [JavaScript](./JavaScript/Binary-Tree-ZigZag-Traversal.js) | _O(n)_    | _O(n)_    | Medium     | Binary Tree                     |      |
-| 129 | [Sum Root to Leaf Numbers](https://leetcode.com/problems/sum-root-to-leaf-numbers/)           | [Java](./Java/sum-root-to-leaf-numbers.java)               | _O(n)_    | _O(logn)_ | Medium     | Binary Tree, Depth First Search |      |
-| 307 | [Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/)           | [Java](./Java/Range-Sum-Query-Mutable.java)                | _O(logn)_ | _O(n)_    | Medium     | Segment Tree                    |      |
+| #   | Title                                                                                             | Solution                                                   | Time      | Space     | Difficulty | Tag                             | Note |
+| --- | ------------------------------------------------------------------------------------------------- | ---------------------------------------------------------- | --------- | --------- | ---------- | ------------------------------- | ---- |
+| 094 | [Binary Tree Inorder Traversal](https://leetcode.com/problems/binary-tree-inorder-traversal/)     | [Java](./Java/binary-tree-inorder-traversal.java)          | _O(n)_    | _O(logn)_ | Medium     | Binary Tree, Stack, HashTable   |      |
+| 144 | [Binary Tree Preorder Traversal](https://leetcode.com/problems/binary-tree-preorder-traversal/)   | [Java](./Java/binary-tree-preorder-traversal.java)         | _O(n)_    | _O(logn)_ | Medium     | Binary Tree, Stack              |      |
+| 145 | [Binary Tree Postorder Traversal](https://leetcode.com/problems/binary-tree-postorder-traversal/) | [Java](./Java/binary-tree-postorder-traversal.java)        | _O(n)_    | _O(logn)_ | Hard       | Binary Tree, Stack              |      |
+| 103 | [ZigZag Level Order](https://leetcode.com/problems/binary-tree-zigzag-level-order-traversal/)     | [JavaScript](./JavaScript/Binary-Tree-ZigZag-Traversal.js) | _O(n)_    | _O(n)_    | Medium     | Binary Tree                     |      |
+| 129 | [Sum Root to Leaf Numbers](https://leetcode.com/problems/sum-root-to-leaf-numbers/)               | [Java](./Java/sum-root-to-leaf-numbers.java)               | _O(n)_    | _O(logn)_ | Medium     | Binary Tree, Depth First Search |      |
+| 307 | [Range Sum Query - Mutable](https://leetcode.com/problems/range-sum-query-mutable/)               | [Java](./Java/Range-Sum-Query-Mutable.java)                | _O(logn)_ | _O(n)_    | Medium     | Segment Tree                    |      |
 
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