1. Code Question 1
Amazon developers are building a prototype for a regex generator for the given strings. For the prototype version, the regex consists of uppercase English letters, '[' and ']'. Here, a string of characters enclosed in square brackets '[' and ']' matches any of the characters in that string. Also, the string of characters enclosed within '[' and ']' consists of uppercase English letters only with no repetition.
For example:
- "[ABBR]ABC" is not a valid regex as B occurs twice between square brackets.
- "["ABC", "A[A[", "]" and "]ABC" are also not valid regexes as brackets must contain some string, and brackets should also form a balanced bracket sequence.
- "[ABC][BCA]" is a valid regex and matches with "BBCA" and "ABCA", but not with "ABBCA".
- "[ABZ][Q]" is a valid regex and matches with "AQ", "BQ", "CQ", "ZQ" but not with "DQ" or "ZC".
- "[A][C][D]" is a valid regex and matches only with the string "ABCD".
Given 3 strings [b]x, y, and z of length n, find the longest regex which matches both the strings x and y but does not match with the string z. If no regex exists that satisfies the multiple such regex exist output the lexicographically smallest one.
- The length of a regex is the number of characters in it, i.e., including uppercase English letters and '[' and ']'.
- A string p is lexicographically smaller than string q, if p is a prefix of q, is not equal to q, or there exists i such that p_i < q_i and for all j < i, it is satisfied that p_j = q_j. Note that while comparing p_j and q_j, we consider their ASCII values, i.e., '[' and ']' are greater than any uppercase English letters. For example, "ABC" is lexicographically smaller than "BCD" and "ABCDE" but larger than "AAC" and "AACDE".
- The answer string, which is to be returned can turn out to be in the order of 10^6 for larger n's.
Example:
x = "AB", y = "BD", z = "CD"
Regex "[ABCDEFGHIJKLMNOPQRSTUVWXYZ][ABCDEFGHIJKLMNOPQRSTUVWXYZ]" matches with strings "AB" and "BD", but not with string "CD".
Function Description
Complete the function findLongestRegex in the editor below.
findLongestRegex has the following parameters:
- x: a string
- y: a string
- z: a string
Returns
string: the longest lexicographically smallest regex matching x and y but not z, if no such regex exists return -1 as a string.
2. Code Question 2
A team of financial analysts at Amazon closely monitors revenue generated by a newly launched product. They classify a period of one or more consecutive days as a stable-growth period if the revenue generated by the product takes no more than k distinct values over that period.
Given an array revenues of size n, that represents the revenues generated by the new product on n consecutive days, and an integer k, determine the total number of stable growth periods over the n days. Since the answer can be large, return it modulo (10^9 + 7).
Example
Suppose n = 3, k = 1, revenues = [1, 2, 1].
Function Description
Complete the getStablePeriodsCount function in the editor below.
getStablePeriodsCount has the following parameters:
- int revenues[n]: the revenues generated by the new product over n days
- int k: the maximum number of distinct values in a stable growth period
Returns
- int: the number of stable growth periods of the product over n days, modulo (10^9 + 7)
Constraints
- 1 ≤ n ≤ 10^5
- 1 ≤ k ≤ n
- -10^9 ≤ revenues[i] ≤ 10^9
Table Explanation:
| Indices of days | Periods | Distinct Values |
|---|---|---|
| [0] | [1] | 1 |
| [0, 1] | [1, 2] | 2 |
| [0, 1, 2] | [1, 2] | 2 |
| [1] | [2] | 1 |
| [1, 2] | [2, 1] | 2 |
| [2] | [1] | 1 |
There are three periods with k = 1 or fewer distinct values. The number of stable growth periods is therefore 3.
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