java - Reverse A Binary Tree (Left to Right)

Question

(Closed). This question needs to be more focused. It is not currently accepting answers. question from:https://stackoverflow.com/questions/9460255/reverse-a-binary-tree-left-to-right

Answer 1

You can use recursion. We swap the left and right child of a node, in-place, and then do the same for its children:

static void reverseTree(final TreeNode root) {
    final TreeNode temp = root.right;
    root.right = root.left;
    root.left = temp;
    
    if (root.left != null) {
        reverseTree(root.left);
    }
    
    if (root.right != null) {
        reverseTree(root.right);
    }
}

To handle the case where the parameter root may be null:

static void reverseTree(final TreeNode root) {
    if (root == null) {
        return;
    }
    
    final TreeNode temp = root.right;
    root.right = root.left;
    root.left = temp;
    
    reverseTree(root.left);
    
    reverseTree(root.right);
}