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 }

2。非递归

/**

 * 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;

    }

    

}