438. Find All Anagrams in a String

package LeetCode_438

/**
 * 438. Find All Anagrams in a String
 * https://leetcode.com/problems/find-all-anagrams-in-a-string/description/
 *
 * Given a string s and a non-empty string p, find all the start indices of p's anagrams in s.
Strings consists of lowercase English letters only and the length of both strings s and p will not be larger than 20,100.
The order of output does not matter.

Example 1:
Input:
s: "cbaebabacd" p: "abc"
Output:
[0, 6]
Explanation:
The substring with start index = 0 is "cba", which is an anagram of "abc".
The substring with start index = 6 is "bac", which is an anagram of "abc".
 * */
class Solution {
    /**
     * solution: Array+Sliding Window, Time complexity:O(n), Space complexity:O(26)
     * */
    fun findAnagrams(s: String, p: String): List<Int> {
        val result = ArrayList<Int>()
        val window = p.length
        val len = s.length
        if (window == 0 || len == 0) {
            return result
        }
        if (len < window) {
            return result
        }
        var left = 0
        var right = 0
        val hash = IntArray(26)
        val pHasp = IntArray(26)
        while (right < window) {
            hash[s[right] - 'a']++
            pHasp[p[right] - 'a']++
            right++
        }
        //scan remaining len of s
        while (right <= len) {
            if (pHasp contentEquals hash) {
                result.add(left)
            }
            /*
            * keep tracking in window size,
            * for example: cbaebabacd,
            * next track: eba=>bab...
            * */
            if (right != len) {
                hash[s[right] - 'a']++
            }
            right++
            hash[s[left++] - 'a']--
        }
        return result
    }
}