Flatten Binary Tree to Linked List | LeetCode | Java

class Solution { TreeNode prevNode = null; public void flatten(TreeNode root) { if(root==null) return; flatten(root.right); flatten(root.left); root.right = prevNode; root.left = null; prevNode = root; }
}

class Solution { public void flatten(TreeNode root) { if(root==null) return; Stack<TreeNode> stack = new Stack<>(); stack.add(root); while(!stack.isEmpty()){ TreeNode currentNode = stack.pop(); if(currentNode.right!=null) stack.push(currentNode.right); if(currentNode.left!=null) stack.push(currentNode.left); if(!stack.isEmpty()) currentNode.right = stack.peek(); currentNode.left = null; } }
}