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", "AA[C]", "]T" and "JABC" are also not valid regexes as brackets must contain some string, and brackets should also form a balanced bracket sequence.
• "[ABCD][CA]" is a valid regex and matches with "BBCA" and "ABCA", but not with "ABBCA".
• "[ABCZ][Q]" is a valid regex and matches with "AQ", "BQ", "CQ", "ZQ" but not with "DQ" or "ZC".
• "[AB][C][D]" is a valid regex and matches only with the string "ABCD".

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Problem Statement

Given 3 strings x, y, and z of length n, find the longest regex that matches both the strings x and y but does not match with the string z. If no such regex exists, output -1. If multiple such regexes exist, output the lexicographically smallest one.

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Notes

• The length of a regex is the number of characters in it, i.e., including uppercase English alphabets, [ 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 j such that p[j] < q[j] and for all i < j, p[i] = q[i]. Note that while comparing p[j] and q[j], we consider their ASCII values, i.e., [ and ] are greater than uppercase English letters. For example:
  • "ABC" is lexicographically smaller than "BCD".
  • "ABCDE" but larger than "AACD" and "AACDE".
• The answer string, which is to be returned, can turn out to be in the order of 10^6 for larger n.

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Example

Input:

x = "AB"
y = "BD"
z = "CD"

Output:

[ABCDEFGHJKLMNOPQRSTUVWXYZ][ABCDEFGHJKLMNOPQRSTUVWXYZ]

Explanation:
Regex [ABCDEFGHJKLMNOPQRSTUVWXYZ][ABCDEFGHJKLMNOPQRSTUVWXYZ] matches with strings "AB" and "BD", but not with string "CD".

Input:

x = "ABCD"
y = "CODE"
z = "CODE"

Output:

-1

Explanation:
As strings y and z are equal, it is not possible that a regex matches with y but not with z. Hence, the output is -1.

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Function Description

Complete the function findLongestRegex in the editor below.

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.

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Constraints

1. 1 ≤ n ≤ 10^5
2. x, y, and z consist of uppercase English letters only.

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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).

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Example

Suppose n = 3, k = 1, revenues = [1, 2, 1].

Indices of days	Periods	Distinct Values
[0]	[1]	1
[0, 1]	[1, 2]	2
[0, 1, 2]	[1, 2, 1]	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 3.

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Function Description

Complete the getStablePeriodsCount function in the editor below.

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)

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Constraints

1. 1 ≤ n ≤ 10^5
2. 1 ≤ k ≤ n
3. -10^9 ≤ revenues[i] ≤ 10^9

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Example Input and Output

Sample Input 0:

n = 4
revenues = [2, -3, 2, -3]
k = 2

Sample Output 0:

10

Explanation:
Any contiguous period of 1 or more days has 2 or fewer distinct values, thus all 10 subarrays represent a period of stable growth.

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Sample Input 1:

n = 6
revenues = [2, 3, -4, -1, -2, -1]
k = 2

Sample Output 1:

<Output not provided in image>

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