Is Last Substring in Lexicographical Order easy or hard?

LeetCode classifies this problem as Hard because the optimal O(n) solution relies on a non-obvious suffix elimination strategy. Many first attempts use brute force suffix generation or sorting, which leads to O(n^2) or O(n log n) complexity.

Last Substring in Lexicographical Order Python/Java solution

Python and JavaScript implementations usually apply the O(n) two-pointer suffix comparison method because it requires only index arithmetic and character comparisons. C++ and Java implementations sometimes demonstrate suffix array construction for educational purposes.

How to solve Last Substring in Lexicographical Order in O(n)?

Maintain two candidate suffix indices i and j along with an offset k. Compare characters s[i+k] and s[j+k]. When characters differ, discard the smaller suffix by moving its pointer forward past the compared segment and reset k. Continue until one candidate reaches the end; the remaining index marks the largest suffix.

What is the best approach for Last Substring in Lexicographical Order?

The most efficient approach uses a two-pointer suffix comparison technique. Two candidate starting indices are compared while skipping dominated suffixes, ensuring each character is processed at most a few times. This yields O(n) time and O(1) space, making it the optimal solution for large strings.

Is Last Substring in Lexicographical Order asked at Google/Amazon/Meta?

Variants of suffix comparison and lexicographically maximum substring problems appear in interviews at large tech companies including Google and Amazon. These companies often test understanding of linear-time string algorithms, suffix structures, and pointer-based comparisons.

What data structure is used in Last Substring in Lexicographical Order?

The optimal solution relies mainly on pointer indices and character comparisons rather than complex data structures. An alternative solution uses a suffix array along with an optional LCP array, which are classic structures in advanced string processing.

What is the time complexity of Last Substring in Lexicographical Order?

The optimal two-pointer algorithm runs in O(n) time with O(1) additional space. A suffix array based solution typically takes O(n log n) time and O(n) space due to sorting suffix ranks. Both methods produce the same result but the linear scan is faster.

1163. Last Substring in Lexicographical Order - Practice Online

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.