https://oj.leetcode.com/problems/populating-next-right-pointers-in-each-node/
https://oj.leetcode.com/problems/remove-duplicates-from-sorted-list/
https://oj.leetcode.com/problems/roman-to-integer/
https://oj.leetcode.com/problems/climbing-stairs/
https://oj.leetcode.com/problems/maximum-subarray/