题解 | #将升序数组转化为平衡二叉搜索树#

简单的递归题

/**
 * struct TreeNode {
 *    int val;
 *    struct TreeNode *left;
 *    struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param num int整型vector 
     * @return TreeNode类
     */

    TreeNode* sortedArrayToBST(vector<int>& num) {
        // write code here
        return  dfs(num, 0, num.size() - 1);
    }
    TreeNode* dfs(vector<int> & num, int l, int r)
    {
        if(l > r) return nullptr;
        if(l == r) return new TreeNode(num[l]);
        auto root = new TreeNode(num[(l + r + 1) >> 1]);
        root->left = dfs(num, l, ((l + r + 1) >> 1) - 1);
        root->right = dfs(num, ((l + r + 1) >> 1) + 1, r);
        return root;
    }
};