6.5二叉树(654.最大二叉树）

/**
 * 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* constructMaximumBinaryTree(vector<int>& nums) {
        return build(nums, 0, nums.size());
    }

    TreeNode* build(vector<int>& nums, int left, int right){
        if(left>=right) return nullptr;
        int max_index = left;

        for(int i = left; i <right; i++){
            if(nums[i] > nums[max_index]){
                max_index = i;
            }
        }

        TreeNode* node = new TreeNode(nums[max_index]);
        
        node->left = build(nums, left, max_index);

        node->right = build(nums, max_index+1, right);

        return node;
    }
};

今天除了这道题，还把昨天的题目优化了一下，感觉还是不错的哦。