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Solve sliding-window and disjoint-string-pairs tasks

NetflixSoftware Engineer · Technical Screen
MediumSoftware EngineerTechnical ScreenCoding & Algorithms

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This question tests the ability to combine sliding window techniques with bit manipulation or frequency counting to identify pairs of substrings that share no common characters.

Problem Statement

Given a string s, find the maximum product of the lengths of two disjoint substrings s[i...j] and s[k...m] such that they share no common characters. Two substrings are disjoint if their index ranges do not overlap. If it is impossible to find such a pair, return 0.

Function Signature

def max_product_disjoint_substrings(s: str) -> int:

Constraints

  • 2 <= len(s) <= 100
  • The string contains only lowercase English letters.

Examples

Example 1: Input: s = "abcde" Output: 4 Explanation: We can pick "ab" (length 2) and "cd" (length 2). Their product is 4. They are disjoint and share no common characters.

Example 2: Input: s = "aaaaa" Output: 0 Explanation: Any two disjoint substrings will contain the character 'a', so no pair can satisfy the condition.

Considerations

  • Focus on efficiently checking the 'no common characters' condition.
  • Ensure the index ranges [i, j] and [k, m] are strictly separated (i.e., j < k or m < i).

Hints

Hint 1

Represent the set of characters present in any substring using a bitmask of length 26.

Hint 2

Precompute all possible substrings and their associated bitmasks and lengths, storing them in a list or hash map.

Hint 3

Iterate through all pairs of stored substrings, checking if their bitmasks have a bitwise AND equal to zero and ensuring their indices do not overlap.

Follow-up questions

  • How would your approach change if the string length was increased to 10,000?
  • Can you optimize the storage if many substrings share the same bitmask?
  • How would you modify the algorithm if we wanted to find the maximum product of three disjoint substrings with no common characters?