https://oj.leetcode.com/problems/balanced-binary-tree/
https://oj.leetcode.com/problems/convert-sorted-array-to-binary-search-tree/
https://oj.leetcode.com/problems/convert-sorted-list-to-binary-search-tree/
https://oj.leetcode.com/problems/minimum-depth-of-binary-tree/
https://oj.leetcode.com/problems/path-sum/
https://oj.leetcode.com/problems/path-sum-ii/