94. Binary Tree Inorder Traversal

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LeetCode

Recursion

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    void inorderTraversalUtil(TreeNode root,List<Integer> ls){
        if(root==null) return;
        inorderTraversalUtil(root.left,ls);
        ls.add(root.val);
        inorderTraversalUtil(root.right,ls);
    }
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> ls=new LinkedList<>();
        inorderTraversalUtil(root,ls);
        return ls;
    }
}

Morris Traversal

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public List<Integer> inorderTraversal(TreeNode root) {
        List<Integer> result=new ArrayList<>();
        TreeNode curr=root;  
        while(curr!=null){
            if(curr.left==null) {
                result.add(curr.val);
                curr=curr.right;
            }
            else{
                TreeNode pre=curr.left;
                while(pre.right!=null){
                    pre=pre.right;
                }
                pre.right=curr;
                TreeNode temp=curr;
                curr=curr.left;
                temp.left=null;  
            }    
        }
        return result;
    }
}

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