Given a string s, return the last substring of s in lexicographical order. Example 1: Input: s = "abab" Output: "bab" Explanation: The substrings are ["a", "ab", "aba", "abab", "b", "ba", "bab"]. The lexicographically maximum substring is "bab". Example 2: Input: s = "leetcode" Output: "tcode" Constraints: 1 <= s.length <= 4 * 105 s contains only lowercase English letters.