Longest Common Prefix in DSA C - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is the Longest Common Prefix (LCP) in a list of strings?

The Longest Common Prefix is the longest starting substring that is common to all strings in the list.

beginner

How can you find the Longest Common Prefix by comparing characters?

Compare characters of the first string with the same position characters of all other strings until a mismatch is found or the end of the shortest string is reached.

intermediate

Why is it efficient to use the first string as a reference when finding the LCP?

Because the prefix must be part of the first string, using it as a reference reduces unnecessary comparisons and helps stop early when a mismatch occurs.

intermediate

What is the time complexity of the simple character-by-character LCP algorithm?

The time complexity is O(S), where S is the sum of all characters in all strings because each character is compared at most once.

beginner

What should the function return if the input list of strings is empty?

It should return an empty string since there is no common prefix without any strings.

What does the Longest Common Prefix represent in a list of strings?

A The longest substring common anywhere in all strings

B The longest substring common at the end of all strings

C The shortest string in the list

D The longest substring common at the start of all strings

The Longest Common Prefix is the longest starting substring common to all strings.

If one string in the list is empty, what is the Longest Common Prefix?

A Empty string

B The first string

C The longest string

D The shortest non-empty string

If any string is empty, the common prefix must be empty.

Which approach is simplest to find the Longest Common Prefix?

A Compare characters of the first string with all others until mismatch

B Sort strings and compare first and last only

C Use hash maps to count characters

D Reverse all strings and compare

Comparing characters of the first string with others until mismatch is the straightforward method.

What is the worst-case time complexity of the character-by-character LCP method?

A O(N^2), where N is number of strings

B O(log N)

C O(S), where S is total characters in all strings

D O(1)

Each character is compared at most once, so complexity is proportional to total characters.

If the first two strings are "flower" and "flow", what is their common prefix?

A flower

B flow

C flo

D fl

The longest common prefix is "flow" because it matches the start of both strings.

Explain how to find the Longest Common Prefix in a list of strings using character comparison.

Think about checking each character position across all strings.

Describe edge cases to consider when implementing Longest Common Prefix.

Consider what happens when input is minimal or has no overlap.