leetcode 94. 二叉树的中序遍历

给定一个二叉树，返回它的中序 遍历。

示例:

输入: [1,null,2,3]
1
\
2
/
3

输出: [1,3,2]

//迭代算法
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        if(root==null)return list;
        Stack<TreeNode> stack = new Stack<TreeNode>();
        stack.push(root);
        TreeNode cur = root.left;
        while(cur!=null||!stack.empty()){
            while(cur!=null){
                stack.push(cur);
                cur=cur.left;
            }
            TreeNode tmpnode = stack.pop();
            list.add(tmpnode.val);
            cur = tmpnode.right;
        }
        return list;
    }
}


 //递归算法
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list = new ArrayList<Integer>();
        if(root==null)return list;
        inorder(root,list);
        return list;
    }
    public void inorder(TreeNode node,List<Integer> list){
        if(node.left!=null)inorder(node.left,list);
        list.add(node.val);
        if(node.right!=null)inorder(node.right,list);
    }
}