纸上得来终觉浅 绝知此事要躬行

纸上得来终觉浅 绝知此事要躬行

  1. Maximum Binary Tree II
    Solved
    Medium
    Topics
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    A maximum tree is a tree where every node has a value greater than any other value in its subtree.

You are given the root of a maximum binary tree and an integer val.

Just as in the previous problem, the given tree was constructed from a list a (root = Construct(a)) recursively with the following Construct(a) routine:

If a is empty, return null.
Otherwise, let a[i] be the largest element of a. Create a root node with the value a[i].
The left child of root will be Construct([a[0], a[1], …, a[i - 1]]).
The right child of root will be Construct([a[i + 1], a[i + 2], …, a[a.length - 1]]).
Return root.
Note that we were not given a directly, only a root node root = Construct(a).

Suppose b is a copy of a with the value val appended to it. It is guaranteed that b has unique values.

Return Construct(b).

Example 1:

Input: root = [4,1,3,null,null,2], val = 5
Output: [5,4,null,1,3,null,null,2]
Explanation: a = [1,4,2,3], b = [1,4,2,3,5]
Example 2:

Input: root = [5,2,4,null,1], val = 3
Output: [5,2,4,null,1,null,3]
Explanation: a = [2,1,5,4], b = [2,1,5,4,3]
Example 3:

Input: root = [5,2,3,null,1], val = 4
Output: [5,2,4,null,1,3]
Explanation: a = [2,1,5,3], b = [2,1,5,3,4]

Constraints:

The number of nodes in the tree is in the range [1, 100].
1 <= Node.val <= 100
All the values of the tree are unique.
1 <= val <= 100

解法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:
    TreeNode* insertIntoMaxTree(TreeNode* root, int val) {
        TreeNode *newNode = new TreeNode(val);
        if (!root) return newNode;
        if (val > root->val) {
            newNode->left = root;
            return newNode;
        } else {
            if (root->right) {
                if (val > root->right->val) {
                    newNode->left = root->right;
                    root->right = newNode;                    
                } else {
                    root->right = insertIntoMaxTree(root->right, val);
                }
            } else {
                root->right = newNode;
            }
        }
        return root;
    }
};

二刷:事实上,如果val < root->val,那么val的节点肯定是加在root的右子树。递归即可。

class Solution {
public:
    TreeNode* insertIntoMaxTree(TreeNode* root, int val) {
        TreeNode *newNode = new TreeNode(val);
        if (!root) return newNode;
        if (val > root->val) {
            newNode->left = root;
            return newNode;
        } else {
            root->right = insertIntoMaxTree(root->right, val);
        }
        return root;
    }
};
01-30 04:56