ama-non

Example:

input:

output:

思路一：递归

/**
 * 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;
    }
};

思路二：层次遍历(迭代)

/**
 * 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) {
        std::stack<TreeNode*> stk;
        stk.push(root);
        
        while (!stk.empty()) {
            TreeNode *cur_root = stk.top();
            stk.pop();
            if (cur_root) {
                stk.push(cur_root->left);
                stk.push(cur_root->right);
                std::swap(cur_root->left, cur_root->right);
            }
        }
        
        return root;
    }
};