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 1: Array + Sliding Window, Time complexity:O(n), Space complexity:O(26)
    * */
    fun findAnagrams(s: String, p: String): List<Int> {
        val result = ArrayList<Int>()
        if (p.length > s.length) {
            return result
        }
        val sMap = IntArray(26)
        val pMap = IntArray(26)
        val sLength = s.length
        val pLength = p.length
        for (c in p) {
            pMap[c - 'a']++
        }
        for (i in 0 until sLength) {
            if (i >= pLength) {
                //remove the element out of window to keep tracking compare, the length of this window is pLength
                sMap[s[i - pLength] - 'a']--
            }
            sMap[s[i] - 'a']++
            if (sMap contentEquals pMap) {
                result.add(i + 1 - pLength)
            }
        }
        return result
    }
}