From c32c20d23f8c6a1156013ffed4f2620fb90ba844 Mon Sep 17 00:00:00 2001
From: alpha19976 <chenda1996@gmail.com>
Date: Fri, 2 Nov 2018 19:06:03 +0800
Subject: [PATCH] Create f.java

---
 f.java | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)
 create mode 100644 f.java

diff --git a/f.java b/f.java
new file mode 100644
index 0000000..3fc09ac
--- /dev/null
+++ b/f.java
@@ -0,0 +1,51 @@
+Pre Order Traverse
+public List<Integer> preorderTraversal(TreeNode root) {
+    List<Integer> result = new ArrayList<>();
+    Deque<TreeNode> stack = new ArrayDeque<>();
+    TreeNode p = root;
+    while(!stack.isEmpty() || p != null) {
+        if(p != null) {
+            stack.push(p);
+            result.add(p.val);  // Add before going to children
+            p = p.left;
+        } else {
+            TreeNode node = stack.pop();
+            p = node.right;   
+        }
+    }
+    return result;
+}
+In Order Traverse
+public List<Integer> inorderTraversal(TreeNode root) {
+    List<Integer> result = new ArrayList<>();
+    Deque<TreeNode> stack = new ArrayDeque<>();
+    TreeNode p = root;
+    while(!stack.isEmpty() || p != null) {
+        if(p != null) {
+            stack.push(p);
+            p = p.left;
+        } else {
+            TreeNode node = stack.pop();
+            result.add(node.val);  // Add after all left children
+            p = node.right;   
+        }
+    }
+    return result;
+}
+Post Order Traverse
+public List<Integer> postorderTraversal(TreeNode root) {
+    LinkedList<Integer> result = new LinkedList<>();
+    Deque<TreeNode> stack = new ArrayDeque<>();
+    TreeNode p = root;
+    while(!stack.isEmpty() || p != null) {
+        if(p != null) {
+            stack.push(p);
+            result.addFirst(p.val);  // Reverse the process of preorder
+            p = p.right;             // Reverse the process of preorder
+        } else {
+            TreeNode node = stack.pop();
+            p = node.left;           // Reverse the process of preorder
+        }
+    }
+    return result;
+}