Is Make Three Strings Equal easy or hard?

Make Three Strings Equal is classified as an Easy problem. The key insight is recognizing that deleting from the end forces the final result to be a common prefix. Once that observation is made, the implementation becomes a straightforward linear scan.

Make Three Strings Equal Python/Java solution

In Python or Java, iterate with an index while characters match across all three strings. Stop when a mismatch occurs or one string ends. Calculate the remaining characters in each string and sum them to get the number of deletions. The implementation is short and runs in O(n) time.

How to solve Make Three Strings Equal in O(n)?

Iterate through the three strings simultaneously and determine the longest common prefix length k. Once a mismatch appears, stop the scan. The number of deletions required is (len(s1) - k) + (len(s2) - k) + (len(s3) - k). This single pass ensures linear time complexity.

What is the best approach for Make Three Strings Equal?

The best approach is finding the longest common prefix among the three strings. Since deletions are allowed only from the end, the final equal string must be a shared prefix. Scan all three strings simultaneously until characters differ, then compute the number of deletions needed. This runs in O(n) time and O(1) space.

Is Make Three Strings Equal asked at Google/Amazon/Meta?

Problems based on longest common prefix and constrained string deletions appear frequently in interviews at companies like Amazon, Google, and Meta. While this exact problem may vary in wording, the underlying pattern—prefix comparison and greedy trimming—is a common string interview concept.

What data structure is used in Make Three Strings Equal?

The problem mainly uses basic string traversal with index pointers. No advanced data structures are required. The solution relies on comparing characters across multiple strings and computing prefix lengths.

What is the time complexity of Make Three Strings Equal?

The optimal solution runs in O(n) time where n is the length of the shortest string. The algorithm compares characters across the three strings once to find their longest common prefix. Space complexity remains O(1) because only counters and indices are used.

Description Hints 1 Solution Video 6:29

2937. Make Three Strings Equal

Easy45.3% acceptance1 company

You are given three strings: s1, s2, and s3. In one operation you can choose one of these strings and delete its rightmost character. Note that you cannot completely empty a string.

Return the minimum number of operations required to make the strings equal. If it is impossible to make them equal, return -1.

Example 1:

Input: s1 = "abc", s2 = "abb", s3 = "ab"

Output: 2

Explanation: Deleting the rightmost character from both s1 and s2 will result in three equal strings.

Example 2:

Input: s1 = "dac", s2 = "bac", s3 = "cac"

Output: -1

Explanation: Since the first letters of s1 and s2 differ, they cannot be made equal.

Constraints:

1 <= s1.length, s2.length, s3.length <= 100
s1, s2 and s3 consist only of lowercase English letters.

Asked at 1 company

Amazon

Topics

String

Hints open one at a time

Hint 1

Calculate the length of the longest common prefix of the 3 strings.

6:29

Still stuck?Read 3 approaches, or watch a walkthrough.

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