Invert Binary Tree - https://twitter.com/mxcl/status/608682016205344768

Invert Binary Tree - C

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     struct TreeNode *left;
 *     struct TreeNode *right;
 * };
 */
struct TreeNode* invertTree(struct TreeNode* root) {
    if (root) {
        root->left = invertTree(root->left), root->right = invertTree(root->right);
        const struct TreeNode* tmp = root->left;
        root->left = root->right;
        root->right = tmp;
    }
    return root;
}

Invert Binary Tree - C++

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
  public:
    TreeNode* invertTree(TreeNode* root) {
        if (root) {
        root->left = invertTree(root->left), root->right = invertTree(root->right);
        std::swap(root->left, root->right);
    }
    return root;
  }
};

Invert Binary Tree - Java

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    public TreeNode invertTree(TreeNode root) {
        if (root != null) {
            root.left = invertTree(root.left);
            root.right = invertTree(root.right);
            TreeNode tmp = root.left;
            root.left = root.right;
            root.right = tmp;
        }
        return root;
    }
}

Invert Binary Tree - Python

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, x):
#         self.val = x
#         self.left = None
#         self.right = None

class Solution:
    # @param {TreeNode} root
    # @return {TreeNode}
    def invertTree(self, root):
        if root:
            root.left, root.right = self.invertTree(root.right), self.invertTree(root.left)
        return root

Invert Binary Tree - Swift

/**
* Definition for singly-linked list.
* class TreeNode {
*   var val:    Int?
*   var left:   TreeNode?
*   var right:  TreeNode?
*
*   init(val aVal: Int?, left aLeft: TreeNode? = nil, right aRight: TreeNode? = nil) {
*       val     = aVal
*       left    = aLeft
*       right   = aRight
*   }
* }
*/

func invertTree(root: TreeNode?) -> TreeNode? {
    if root != nil {
        (root!.right, root!.left) = (invertTree(root!.left), invertTree(root!.right))
    }
    return root
}

// invertTree(tree)