[Pattern: Sliding Window][Hard] String Anagrams

[Pei Yao-Chang]

Given a string and a pattern, find all anagrams of the pattern in the given string.

Every anagram is a permutation of a string. As we know, when we are not allowed to repeat characters while finding permutations of a string, we get N!N! permutations (or anagrams) of a string having NN characters. For example, here are the six anagrams of the string “abc”:

abc
acb
bac
bca
cab
cba
Write a function to return a list of starting indices of the anagrams of the pattern in the given string.

Example 1:

Input: String="ppqp", Pattern="pq"
Output: [1, 2]
Explanation: The two anagrams of the pattern in the given string are "pq" and "qp".

Example 2:

Input: String="abbcabc", Pattern="abc"
Output: [2, 3, 4]
Explanation: The three anagrams of the pattern in the given string are "bca", "cab", and "abc".