226. Invert Binary Tree

/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*非递归
*/
class Solution {
public:
TreeNode* invertTree(TreeNode* root) {
if(!root) return root;
stack<TreeNode*> s1;
s1.push(root);
while(!s1.empty())
{
TreeNode* a=s1.top();
TreeNode* b=a->left;
a->left=a->right;
a->right=b;
s1.pop();
if(a->left) s1.push(a->left);
if(a->right) s1.push(a->right);
}
return root;
}
};

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