Count Substrings That Can Be Rearranged to Contain a String II

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You are given two strings word1 and word2.

A string x is called valid if x can be rearranged to have word2 as a prefix.

Return the total number of valid substrings of word1.

Note that the memory limits in this problem are smaller than usual, so you must implement a solution with a linear runtime complexity.

 

Example 1:

Input: word1 = "bcca", word2 = "abc"

Output: 1

Explanation:

The only valid substring is "bcca" which can be rearranged to "abcc" having "abc" as a prefix.

Example 2:

Input: word1 = "abcabc", word2 = "abc"

Output: 10

Explanation:

All the substrings except substrings of size 1 and size 2 are valid.

Example 3:

Input: word1 = "abcabc", word2 = "aaabc"

Output: 0

 

Constraints:

• 1 <= word1.length <= 106
• 1 <= word2.length <= 104
• word1 and word2 consist only of lowercase English letters.