剑指offer树27.二叉树的镜像

Posted 2021-03-02 trevo

二叉树的镜像

递归法

递归的先序遍历二叉树，交换每个节点的左右子节点，即可生成二叉树的镜像

/**
 * 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* mirrorTree(TreeNode* root) {
        if(root == nullptr) return nullptr;
        TreeNode *tmp = root->left;
        root->left = mirrorTree(root->right);
        root->right = mirrorTree(tmp);
        return root;
    }
};

辅助栈/队列

利用栈或队列遍历树的所有节点，交换每个节点的左右子节点

/**
 * 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* mirrorTree(TreeNode* root) {
        stack<TreeNode*> s;
        s.push(root);
        while (!s.empty()) {
            TreeNode* node = s.top();
            s.pop();
            if (node == NULL) {
                continue;
            }
            swap(node->left, node->right);
            s.push(node->left); 
            s.push(node->right);
        }
        return root;
    }
};

class Solution {
public:
    TreeNode* mirrorTree(TreeNode* root) {
        queue<TreeNode*> q;
        q.push(root);
        while (!q.empty()) {
            TreeNode* node = q.front();
            q.pop();
            if (node == NULL) {
                continue;
            }
            swap(node->left, node->right);
            q.push(node->left);
            q.push(node->right);
        }
        return root;
    }
};