226. Invert Binary Tree

Invert a binary tree.

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

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

Trivia:
This problem was inspired by this original tweet by Max Howell:

方法一：递归

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     TreeNode* invertTree(TreeNode* root) {
13         if(root)
14         {
15             invertTree(root->left);
16             invertTree(root->right);
17             swap(root->left,root->right);
18         }
19         return root;
20     }
21 };

方法二：非递归，栈

 1 class Solution {
 2 public:
 3     TreeNode* invertTree(TreeNode* root) {
 4         stack<TreeNode*>stk;
 5         stk.push(root);
 6         while(!stk.empty())
 7         {
 8             TreeNode*tmp=stk.top();
 9             stk.pop();
10             if(tmp)//tmp可能为空
11             {
12                 stk.push(tmp->left);
13                 stk.push(tmp->right);
14                 swap(tmp->left,tmp->right);
15             }
16             
17         }
18         return root;
19     }
20 };

posted on 2017-09-26 11:41 王早阅读(76) 评论(0) 编辑收藏举报