226. Invert Binary Tree

Problem:

Invert a binary tree.

Invert a binary tree. 
     4
   /   \
  2     7
 / \   / \
1   3 6   9

to

     4
   /   \
  7     2
 / \   / \
9   6 3   1

One Possible Solution:

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