中序遍历 递归与非递归

 1 /**
 2  * Definition for binary tree
 3  * public class TreeNode {
 4  *     int val;
 5  *     TreeNode left;
 6  *     TreeNode right;
 7  *     TreeNode(int x) { val = x; }
 8  * }
 9  */
10 public class Solution {
11     
12     public List<Integer> inorderTraversal(TreeNode root) {
13         ArrayList<Integer> arr=new ArrayList<Integer>();
14         if(root==null) return arr;
15        inorder(root,arr);
16        return (List)arr;
17         
18         
19     }
20      public void inorder(TreeNode root,ArrayList<Integer> arr) {
21         if(root!=null)
22         {
23            inorder(root.left,arr);
24            arr.add(root.val);
25            inorder(root.right,arr);
26         }
27 
28         
29         
30     }
31 }

/**
 * Definition for binary tree
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    
    public List<Integer> inorderTraversal(TreeNode root) {
        ArrayList<Integer> arr=new ArrayList<Integer>();
        if(root==null) return arr;
       Stack<TreeNode> s=new Stack<TreeNode>();
       TreeNode t=root;
       while(!s.isEmpty()||t!=null)
       {
           while(t!=null)
           {
               s.push(t);
               t=t.left;
           }
           
           if(s!=null)
           {
               t=s.pop();
              arr.add(t.val);
              t=t.right;
               
               
           }
           
           
       }
        
        return arr;
    }
    
}