【leetcode】94. Binary Tree Inorder Traversal【java】

Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree [1,null,2,3],

   1
    \
     2
    /
   3

return [1,3,2].

Note: Recursive solution is trivial, could you do it iteratively?

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List inorderTraversal(TreeNode root) {
        //非递归 中序遍历二叉树 （先左子树  再根节点  再右子树）
        List list =new ArrayList();
        Stack stack=new Stack();
        if(root==null) return list;
        while(root!=null){
            stack.push(root);
            root=root.left;
            while(root==null){
                if(stack.empty()) {
                    return list;
                }
                root=stack.pop();
                list.add(root.val);
                root=root.right;
            }
        }
        return list;

        //递归 中序遍历二叉树
        /*List list = new ArrayList();
        addNode(list, root);
        return list;
    }
    public void addNode(List list, TreeNode root){
        if (root == null){
            return;
        }
        addNode(list, root.left);
        list.add(root.val);
        addNode(list, root.right);**/
    }
}

非递归  2017-1-1更改

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public List inorderTraversal(TreeNode root) {
        List result = new ArrayList();
        Stack stack = new Stack();
        TreeNode cur = root;
        while (!stack.isEmpty() || cur != null){
            if (cur != null){
                stack.push(cur);
                cur = cur.left;
            } else{
                TreeNode p = stack.pop();
                result.add(p.val);
                cur = p.right;
            }
        }
        return result;
    }
}