108.convert-sorted-array-to-binary-search-tree.cpp

/**
 * 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 _sortedArrayToBST(nums, 0, nums.size());
    }
private:
    TreeNode* _sortedArrayToBST(vector<int>& nums, int l, int r) {
        if(l >= r) return NULL;
        int mid = l + (r-l)/2;
        TreeNode* root = new TreeNode(nums[mid]);
        root->left = _sortedArrayToBST(nums, l, mid);
        root->right = _sortedArrayToBST(nums, mid+1, r);
        return root;
    }

};