1898 - Maximum Number of Removable Characters.

Medium

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, "abcacb" becomes "accb".

"ab" is a subsequence of "accb".

If we remove the characters at indices 3, 1, and 0, "abcacb" 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, "abcbddddd" becomes "abcddddd".

"abcd" is a subsequence of "abcddddd".

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:

• <code>1 <= p.length <= s.length <= 10⁵</code>

• 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.