226. Invert Binary Tree

1.問題

• 反轉binary tree

2.想法

• Recursion + swap

  • 由下到上, 交換child node

3.程式碼

/**
 * 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) {
            return root;
        }
        
        return swap(root);
    }
private:
    TreeNode* swap(TreeNode* root) {
        if (!root) {
            return root;
        }
        
        TreeNode* tmp = swap(root->left);
        root->left = swap(root->right);
        root->right = tmp;
        
        return root;
    }
};

4.Performance