LeetCode 654. 最大二叉树

654. 最大二叉树

这道题有点像二分法，关键就是对于每个根节点找到当前 nums 中的最大值和对应的索引，然后递归调用左右数组构造左右子树即可

/**
 * 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() - 1);
    }
    
    TreeNode* build(vector<int>& nums, int low, int high){
        if (low > high) return nullptr;

        int index = -1, max_val = INT_MIN;
        for (int i = low; i <= high; i++)
        {
            if (max_val < nums[i])
            {
                max_val = nums[i];
                index = i;
            }
        }

        TreeNode* root = new TreeNode(max_val);
        root->left = build(nums, low, index - 1);
        root->right = build(nums, index + 1, high);
        return root;
    }
};