1898. Maximum Number of Removable Characters

https://leetcode.com/problems/maximum-number-of-removable-characters

Description

You are given two strings s and p where p is a subsequence of s. You are also given a distinct 0-indexed integer array removable containing a subset of indices of s (s is also 0-indexed).

You want to choose an integer k (0 <= k <= removable.length) such that, after removing k characters from s using the first k indices in removable, p is still a subsequence of s. More formally, you will mark the character at s[removable[i]] for each 0 <= i < k, then remove all marked characters and check if p is still a subsequence.

Return the maximum k you can choose such that p is still a subsequence of s after the removals.

A subsequence of a string is a new string generated from the original string with some characters (can be none) deleted without changing the relative order of the remaining characters.

Example 1:

**Input:** s = "abcacb", p = "ab", removable = [3,1,0]
**Output:** 2
**Explanation**: After removing the characters at indices 3 and 1, "a~~**b**~~c~~**a**~~cb" becomes "accb".
"ab" is a subsequence of "**a**cc**b**".
If we remove the characters at indices 3, 1, and 0, "~~**ab**~~c~~**a**~~cb" becomes "ccb", and "ab" is no longer a subsequence.
Hence, the maximum k is 2.

Example 2:

**Input:** s = "abcbddddd", p = "abcd", removable = [3,2,1,4,5,6]
**Output:** 1
**Explanation**: After removing the character at index 3, "abc~~**b**~~ddddd" becomes "abcddddd".
"abcd" is a subsequence of "**abcd**dddd".

Example 3:

**Input:** s = "abcab", p = "abc", removable = [0,1,2,3,4]
**Output:** 0
**Explanation**: If you remove the first index in the array removable, "abc" is no longer a subsequence.

Constraints:

• 1 <= p.length <= s.length <= 105

• 0 <= removable.length < s.length

• 0 <= removable[i] < s.length

• p is a subsequence of s.

• s and p both consist of lowercase English letters.

• The elements in removable are distinct.

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