Leetcode:226. Invert Binary Tree

Description:

Invert a binary tree.

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

to

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

解題思路

遞歸算法：
1、交換根節點的左右子樹。
2、對左右子樹分別執行遞歸反轉 。

代碼

遞歸算法

/**
 * 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) {
            invertTree(root->left);
            invertTree(root->right);
            std::swap(root->left,root->right);
        }
        return root;
    }
};

非遞歸算法

TreeNode* invertTree(TreeNode* root) {  
        queue<TreeNode*> tree_queue;  
        if (root == NULL)  
            return root;  
        tree_queue.push(root);  
        while(tree_queue.size() > 0){  
            TreeNode * pNode = tree_queue.front();  
            tree_queue.pop();  
            TreeNode * pLeft = pNode->left;  
            pNode->left = pNode->right;  
            pNode->right = pLeft;  
            if (pNode->left)  
                tree_queue.push(pNode->left);  
            if (pNode->right)  
                tree_queue.push(pNode->right);  
        }  
        return root;  
    }