LeetCode226. Invert Binary Tree

Invert a binary tree.

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

to

     4   /   \  7     2 / \   / \
9   6 3   1
解法：
TreeNode* invertTree(TreeNode* root) {    if(root==NULL)    return NULL;    TreeNode *temp;    temp=root->left;    root->left=temp;    root->right=temp;    invertTree(root->right);    invertTree(root->left);    return root;    }