Given a non-empty string, encode the string such that its encoded length is the shortest. The encoding rule is: k[encoded_string], where the encoded_string inside the square brackets is being repeated exactly k times. Note: k will be a positive integer. If an encoding process does not make the string shorter, then do not encode it. If there are several solutions, return any of them. Example 1: Input: s = "aaa" Output: "aaa" Explanation: There is no way to encode it such that it is shorter than the input string, so we do not encode it. Example 2: Input: s = "aaaaa" Output: "5[a]" Explanation: "5[a]" is shorter than "aaaaa" by 1 character. Example 3: Input: s = "aaaaaaaaaa" Output: "10[a]" Explanation: "a9[a]" or "9[a]a" are also valid solutions, both of them have the same length = 5, which is the same as "10[a]". Example 4: Input: s = "aabcaabcd" Output: "2[aabc]d" Explanation: "aabc" occurs twice, so one answer can be "2[aabc]d". Example 5: Input: s = "abbbabbbcabbbabbbc" Output: "2[2[abbb]c]" Explanation: "abbbabbbc" occurs twice, but "abbbabbbc" can also be encoded to "2[abbb]c", so one answer can be "2[2[abbb]c]". Constraints: 1 <= s.length <= 150 s consists of only lowercase English letters.