c_cpp 226.反转二叉树

Posted 2021-05-14

/**
 * 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:
    ////自己写的
    ////实际打印和原有的完全相同
    // TreeNode* invertTree(TreeNode* root) {
    //     TreeNode* temp1;
    //     TreeNode* temp2;
    //     TreeNode* temp;
    //     if(root){
    //         temp1 = invertTree(root->left);
    //         temp2 = invertTree(root->right);
            
    //         temp = temp1;
    //         temp1 = temp2;
    //         temp2= temp;
    //     }
    //     return root;
    // }
    
    //参考
    //打印正确
    TreeNode* invertTree(TreeNode* root) {
    if (root) {
        invertTree(root->left);
        invertTree(root->right);
        std::swap(root->left, root->right);
    }
    return root;
}
};

//使用非递归实现
TreeNode* invertTree(TreeNode* root) {
    std::stack<TreeNode*> stk;
    stk.push(root);
    
    while (!stk.empty()) {
        TreeNode* p = stk.top();
        stk.pop();
        if (p) {
            stk.push(p->left);
            stk.push(p->right);
            std::swap(p->left, p->right);
        }
    }
    return root;
}