代码随想录：最大二叉树

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/**
 * 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) {
        if(nums.size()==0)return 0;
        else return build(nums);
    }

    TreeNode* build(vector<int>& nums) {
        if (nums.size() == 0)
            return 0;

        int maxi = -1;
        int index = 0;
        for (int i = 0; i < nums.size(); i++) {
            if (nums[i] > maxi) {
                maxi = nums[i];
                index = i;
            }
        }

        // 最大值即是根节点值
        TreeNode* node = new TreeNode(maxi);

        vector<int> left(nums.begin(), nums.begin() + index);
        vector<int> right(nums.begin() + index + 1, nums.end());

        node->left = build(left);
        node->right = build(right);

        return node;
    }
};