94. 二叉树的中序遍历

package leetcode;

import java.util.ArrayList;
import java.util.List;
import java.util.Stack;

public class demo_94 {
    //递归遍历
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> list=new ArrayList<Integer>();
        order(root, list);
        return list;
    }
    public void order(TreeNode root,List<Integer> list) {
        if(root!=null) {
            order(root.left, list);
            list.add(root.val);
            order(root.right, list);
        }
    }
    
    //非递归遍历
    public List<Integer> inorderTraversal2(TreeNode root) {
        List<Integer> list=new ArrayList<Integer>();
        Stack<TreeNode> stack=new Stack<TreeNode>();
        TreeNode node=root;
        TreeNode temp;
        while(node!=null||!stack.isEmpty()) {
            while(node!=null) {
                stack.push(node);
                node=node.left;
            }
            if(!stack.isEmpty()) {
                temp=stack.pop();
                list.add(temp.val);
                node=temp.right;
            }
        }
        
        return list;
    }
}