/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: the root of binary tree
     * @return: the maximum weight node
     */
    int max_sum;
    TreeNode* max_node;
    
    TreeNode * findSubtree(TreeNode * root) {
        // write your code here
        if(root==NULL)
            return root;
        if(root->left==NULL && root->right==NULL)
            return root;
        max_sum = INT_MIN;
        max_node = NULL;
        dfs(root);
        return max_node;
    }
    int dfs(TreeNode* cur){
        if(cur==NULL)
            return 0;
        int sum = dfs(cur->left)+dfs(cur->right)+cur->val;
        if(sum > max_sum){
            max_sum = sum;
            max_node = cur;
        }
        return sum;
    }
    
};

 

 

 

 

 

 

 计算每个结点的高度并用一个map来存储对应的值，然后将高度从1开始到max_depth 逐层打印出来。

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */


class Solution {
public:
    /*
     * @param root: the root of binary tree
     * @return: collect and remove all leaves
     */
    int max_depth;
    unordered_map<int, vector<int>> depth;
    
    int dfs(TreeNode* cur){
        if(cur == NULL)
            return 0;
        int d = max(dfs(cur->left), dfs(cur->right))+1;
        max_depth = max(max_depth, d);
        depth[d].push_back(cur->val);
        return d;
    }
    vector<vector<int>> findLeaves(TreeNode * root) {
        // write your code here
        vector<vector<int>> ans;
        max_depth = 0;
        dfs(root);
        for(int i=1; i<=max_depth; i++)
            ans.push_back(depth[i]);
        return ans;
    }
};

 

二叉树翻转：

 

 

 

 

 

 

 

 

 

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: the root of binary tree
     * @return: new root
     */
    TreeNode* newRoot;
    TreeNode * upsideDownBinaryTree(TreeNode * root) {
        // write your code here
        if(root == NULL)
            return root;
        dfs(root);
        return newRoot;
    }
    void dfs(TreeNode* cur){
        if(cur->left != NULL){
            dfs(cur->left);
            cur->left->right = cur;
            cur->left->left = cur->right;
            cur->left = NULL;
            cur->right = NULL;
        }
        else
            newRoot = cur;
    }
};