226. Invert Binary Tree

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

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

/**
* 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)
swap(root->left, root->right,root);
return root;
}
void swap(TreeNode* p, TreeNode* q, TreeNode* f){
if (p == NULL && q == NULL){
return;
}
else if (p == NULL && q != NULL){
f->left = q;
f->right = NULL;
p = q;
swap(p->left, p->right, p);
return;
}
else if (p != NULL && q == NULL){
f->right = p;
f->left = NULL;
q = p;
swap(q->left, q->right, q);
return;
}
else{
f->left = q;
f->right = p;
swap(p->left, p->right, p);
swap(q->left, q->right, q);
}
}

};

class Solution {
public:
TreeNode* invertTree(TreeNode* root) {
if (root){
TreeNode* t = root->left;
root->left = root->right;
root->right = t;
invertTree(root->left);
invertTree(root->right);
}
return root;
}
};