Merge pull request #437 from nanaliulei/master

更新二叉树的迭代遍历，增加java代码

problems/二叉树的迭代遍历.md

@@ -155,9 +155,82 @@ public:
 
 ## 其他语言版本
 
-
 Java：
 
+```java
+// 前序遍历顺序：中-左-右，入栈顺序：中-右-左
+class Solution {
+    public List<Integer> preorderTraversal(TreeNode root) {
+        List<Integer> result = new ArrayList<>();
+        if (root == null){
+            return result;
+        }
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(root);
+        while (!stack.isEmpty()){
+            TreeNode node = stack.pop();
+            result.add(node.val);
+            if (node.right != null){
+                stack.push(node.right);
+            }
+            if (node.left != null){
+                stack.push(node.left);
+            }
+        }
+        return result;
+    }
+}
+
+// 中序遍历顺序: 左-中-右 入栈顺序： 左-右
+class Solution {
+    public List<Integer> inorderTraversal(TreeNode root) {
+        List<Integer> result = new ArrayList<>();
+        if (root == null){
+            return result;
+        }
+        Stack<TreeNode> stack = new Stack<>();
+        TreeNode cur = root;
+        while (cur != null || !stack.isEmpty()){
+           if (cur != null){
+               stack.push(cur);
+               cur = cur.left;
+           }else{
+               cur = stack.pop();
+               result.add(cur.val);
+               cur = cur.right;
+           }
+        }
+        return result;
+    }
+}
+
+// 后序遍历顺序 左-右-中 入栈顺序：中-左-右 出栈顺序：中-右-左， 最后翻转结果
+class Solution {
+    public List<Integer> postorderTraversal(TreeNode root) {
+        List<Integer> result = new ArrayList<>();
+        if (root == null){
+            return result;
+        }
+        Stack<TreeNode> stack = new Stack<>();
+        stack.push(root);
+        while (!stack.isEmpty()){
+            TreeNode node = stack.pop();
+            result.add(node.val);
+            if (node.left != null){
+                stack.push(node.left);
+            }
+            if (node.right != null){
+                stack.push(node.right);
+            }
+        }
+        Collections.reverse(result);
+        return result;
+    }
+}
+```
+
+
+
 
 Python：
 ```python3