LeetCode – Invert Binary Tree (Java)

Google: 90% of our engineers use the software you wrote (Homebrew), but you can’t invert a binary tree on a whiteboard so f**k off.

Java Solution 1 - Recursive

public TreeNode invertTree(TreeNode root) {
    if(root!=null){
        helper(root);
    }
 
    return root;    
}
 
public void helper(TreeNode p){
 
    TreeNode temp = p.left;
    p.left = p.right;
    p.right = temp;
 
    if(p.left!=null)
        helper(p.left);
 
    if(p.right!=null)
        helper(p.right);
}

Java Solution 2 - Iterative

public TreeNode invertTree(TreeNode root) {
    LinkedList<TreeNode> queue = new LinkedList<TreeNode>();
 
    if(root!=null){
        queue.add(root);
    }
 
    while(!queue.isEmpty()){
        TreeNode p = queue.poll();
        if(p.left!=null)
            queue.add(p.left);
        if(p.right!=null)
            queue.add(p.right);
 
        TreeNode temp = p.left;
        p.left = p.right;
        p.right = temp;
    }
 
    return root;    
}

If you want someone to read your code, please put the code inside <pre><code> and </code></pre> tags. For example:

<pre><code> 
String foo = "bar";
</code></pre>

Chungho Song

With out helper function

public class Solution { public TreeNode invertTree(TreeNode root) { if( root == null ) return null;
root.left = invertTree(root.left); root.right = invertTree(root.right); TreeNode temp = root.left; root.left = root.right; root.right = temp;
return root; } }
Florian Courtial

I think that the tweet was talking about a min to max heap inverse (or max to min) and not right to left…
Carlos Sousa

Sorry for him, but if you can’t code this algorithm I wouldn’t hire him either… It is one of the easiest questions I’ve seen in a Google interview.
Kai LI

class Solution {
public TreeNode invertTree(TreeNode root) {
if (root==null) return root;
TreeNode leftTmp=root.left;
root.left=invertTree(root.right);
root.right=invertTree(leftTmp);
return root;
}
}
Theja

It’s a tweet from Max Howell, the guy who wrote Homebrew https://twitter.com/mxcl/status/608682016205344768
Wolv

What’s the comment at start?
Roi

Yes there is: when both p.left and p.right are null.
Shailesh Agarwal

There is no exit condition in recursive helper method. So it will be infinite loop.

LeetCode – Invert Binary Tree (Java)

Related posts: