题解 | #将升序数组转化为平衡二叉搜索树#

/**
 * struct TreeNode {
 *	int val;
 *	struct TreeNode *left;
 *	struct TreeNode *right;
 *  TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */

class Solution {
public:
    /**
     * 
     * @param num int整型vector 
     * @return TreeNode类
     */
    TreeNode* sortedArrayToBST(vector<int>& num) {
        // write code here
        if(num.size() == 0){
            return nullptr;
        }
        return create(num, 0, num.size()-1);
    }
    
    TreeNode* create(vector<int>& num, int left, int right){
        if(left > right){
            return nullptr;
        }
        
        int mid = left + (right - left) / 2;
        TreeNode* root = new TreeNode(0);
        root->val = num[mid];
        
        root->left = create(num, left, mid-1);
        root->right = create(num, mid+1, right);
        
        return root;
    }
    
};