LeetCode_226_翻轉二叉樹

題目描述：

翻轉一棵二叉樹。

示例：

輸入：

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

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

算法思想：将二叉樹的右子樹換成左子樹，左子樹換成右子樹

/**
 * 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==NULL)
            return NULL;
        TreeNode* left=invertTree(root->right);
        TreeNode* right=invertTree(root->left);
        root->left=left;
        root->right=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) {}
 * };
 */
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if(root){
            swap(root->left,root->right);//對于兩個指針的指向(位址)進行交換
            invertTree(root->left);
            invertTree(root->right);
        }
        return root;
    }
};