【Leetcode】Binary Tree Inorder Traversal

题目链接：https://leetcode.com/problems/binary-tree-inorder-traversal/

题目：

inorder

For example:

Given binary tree {1,#,2,3},

1 \ 2 / 3

[1,3,2].

Note:

思路：

用栈模拟中序遍历过程

算法：

public List<Integer> inorderTraversal(TreeNode root) {
		List<Integer> list = new ArrayList<Integer>();
		Stack<TreeNode> stack = new Stack<TreeNode>();
		while (root != null || !stack.isEmpty()) {
			if (root != null) {
				stack.push(root);
				root = root.left;  
			} else { //左子树为空，则访问val，且开始遍历右子树
				root = stack.pop();
				list.add(root.val);
				root = root.right;
			}
		}
		return list;
	}