[114. Flatten Binary Tree to Linked List] #leetcode

114.java

class Solution {
    public void flatten(TreeNode root) {
        while (root != null) {
            TreeNode rightNode = root.right;
            root.right = root.left;
            root.left = null;
            // find rightmost node
            TreeNode node = root;
            while (node.right != null) {
                node = node.right;
            }
            node.right = rightNode;
            // move to next right node
            root = root.right;
        }
    }
}

// recursive
class Solution1 {
    private TreeNode successor = null;
    
    public void flatten(TreeNode root) {
        if (root == null) return;
        flatten(root.right);
        flatten(root.left);
        root.right = successor;
        root.left = null;
        successor = root;
    }
}