Is Find Maximum Removals From Source String easy or hard?

The problem is rated Medium because it requires recognizing a monotonic property and combining binary search with subsequence validation. The individual techniques are standard, but identifying that binary search on the answer works is the key insight.

Find Maximum Removals From Source String Python/Java solution

Most implementations follow the same structure: binary search the number of removable indices and validate with a two-pointer subsequence check. The logic is identical across Python, Java, C++, C#, and JavaScript with only syntax differences.

How to solve Find Maximum Removals From Source String in O(n log k)?

Use binary search on the number of characters removed. For each candidate value, mark the first k indices as removed and run a two-pointer subsequence check to see if the pattern still appears in the source string. If it does, increase k; otherwise decrease it. This efficiently finds the maximum valid removal count.

What is the best approach for Find Maximum Removals From Source String?

Binary search with subsequence validation is the most efficient and commonly expected solution. The idea is to binary search the number of removable characters and check whether the pattern remains a subsequence after removing those indices. Each validation uses a two-pointer subsequence scan of the string.

Is Find Maximum Removals From Source String asked at Google/Amazon/Meta?

Problems involving subsequence validation, binary search on answer, and greedy pointer scanning frequently appear in interviews at companies like Google, Amazon, and Meta. Variants of this problem test understanding of binary search over monotonic conditions and string subsequence checks.

What data structure is used in Find Maximum Removals From Source String?

The solution mainly uses arrays or boolean markers to track removed indices, along with two-pointer traversal of the strings. Binary search is applied on the answer space while the subsequence check operates directly on the string characters.

What is the time complexity of Find Maximum Removals From Source String?

The optimal solution runs in O(n log k) time where n is the length of the source string and k is the number of removable indices. Each binary search step performs a linear subsequence check using two pointers. Space complexity is O(n) for tracking removed positions.

Description Hints 2 Solution Video 14:52

3316. Find Maximum Removals From Source String

Medium39.3% acceptance1 company

You are given a string source of size n, a string pattern that is a subsequence of source, and a sorted integer array targetIndices that contains distinct numbers in the range [0, n - 1].

We define an operation as removing a character at an index idx from source such that:

idx is an element of targetIndices.
pattern remains a subsequence of source after removing the character.

Performing an operation does not change the indices of the other characters in source. For example, if you remove 'c' from "acb", the character at index 2 would still be 'b'.

Return the maximum number of operations that can be performed.

Example 1:

Input: source = "abbaa", pattern = "aba", targetIndices = [0,1,2]

Output: 1

Explanation:

We can't remove source[0] but we can do either of these two operations:

Remove source[1], so that source becomes "a_baa".
Remove source[2], so that source becomes "ab_aa".

Example 2:

Input: source = "bcda", pattern = "d", targetIndices = [0,3]

Output: 2

Explanation:

We can remove source[0] and source[3] in two operations.

Example 3:

Input: source = "dda", pattern = "dda", targetIndices = [0,1,2]

Output: 0

Explanation:

We can't remove any character from source.

Example 4:

Input: source = "yeyeykyded", pattern = "yeyyd", targetIndices = [0,2,3,4]

Output: 2

Explanation:

We can remove source[2] and source[3] in two operations.

Constraints:

1 <= n == source.length <= 3 * 10³
1 <= pattern.length <= n
1 <= targetIndices.length <= n
targetIndices is sorted in ascending order.
The input is generated such that targetIndices contains distinct elements in the range [0, n - 1].
source and pattern consist only of lowercase English letters.
The input is generated such that pattern appears as a subsequence in source.

Asked at 1 company

Google

Topics

Hints open one at a time

Hint 1

Use dynamic programming.

Hint 2

At each index in targetIndices, make the choice to remove or not remove the character.

14:52

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

Open solution

3316. Find Maximum Removals From Source String

Asked at 1 company

Topics

Hints open one at a time

Similar problems