01.invertTree.cpp

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */

//Recursive
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if(!root) return NULL;
        
        auto l = invertTree(root->left);
        auto r = invertTree(root->right);
        
        root->left = r;
        root->right = l;
        
        return root;
    }
};

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */


//Iterative
class Solution {
public:
    TreeNode* invertTree(TreeNode* root) {
        if(!root) return NULL;
        
        queue<TreeNode*> qu;
        qu.push(root);
        
        while(!qu.empty()){
            auto current = qu.front();
            qu.pop();
            if(current->left) qu.push(current->left);
            if(current->right) qu.push(current->right);
            
            auto tmp = current->left;
            current->left = current->right;
            current->right = tmp;
        }
        return root;
    }
};