LeetCode(108)将有序数组转换为二叉搜索树

思路：分而治之

/**
 * 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* sortedArrayToBST(vector<int>& nums) {
        return BST(nums,0,nums.size()-1);
    }
    TreeNode* BST(vector<int>&nums,int head,int tail){
        if(head>tail)return NULL;
        int mid = (head+tail)/2;
        TreeNode*h = new TreeNode(nums[mid]);
        h->left = BST(nums,head,mid-1);
        h->right = BST(nums,mid+1,tail);
        return h;
    }
};