leetcode之二叉树

2022.2.15 leetcode刷题——树

/**
 * 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==NULL)
        {
            return root;
        }

        TreeNode* temp = root->left;
        root->left=root->right;
        root->right=temp;
        mirrorTree(root->left);
        mirrorTree(root->right);
        return root;
    }
};

后序递归：
/**
 * 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) {}
 * };
 */
class Solution {
public:
    int maxDepth(TreeNode* root) {
        if(root==NULL)
        {
            return 0;
        }
        int res1 = maxDepth(root->left);
        int res2 = maxDepth(root->right);
        return max(res1,res2)+1;
    }
};

/**
 * 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) {}
 * };
 */
class Solution {
public:
    int depth = 0;
    int minDepth(TreeNode* root) {
        if(root==nullptr)
        {
            return 0;
        }
        if(root->left==nullptr && root->right==nullptr )
        {
            depth= 1;
        }
        if(root->left==nullptr && root->right!=nullptr )
        {
            depth = 1+minDepth(root->right);
        }
        if(root->left!=nullptr && root->right==nullptr )
        {
            depth = 1+minDepth(root->left);
        }
        if(root->left!=nullptr && root->right!=nullptr )
        {
            depth = 1+min(minDepth(root->right),minDepth(root->left));
        }
        return depth;
    }
};

二叉树的层序遍历：

/**
 * 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:
    vector<vector<int>> levelOrder(TreeNode* root) {
        vector<vector<int>> result;
        if(root==NULL)
        {
            return result;
        }
        vector<int> temp_result;
        queue<TreeNode*> myque;
        myque.push(root);

        while(!myque.empty())
        {
            int size=myque.size();
            for(int i=0;i<size;i++)
            {
                TreeNode* temp = myque.front();
                myque.pop();
                temp_result.push_back(temp->val);
                if(temp->left)
                {
                    myque.push(temp->left);
                }
                if(temp->right)
                {
                    myque.push(temp->right);
                }
            }
            result.push_back(temp_result);
            temp_result.clear();
        }
        return result;

    }
};