Leetcode #438: Find All Anagrams in a String

func findAnagrams(_ s: String, _ p: String) -> [Int] {
    if p.count > s.count {
        return []
    }
    var pDict = Array(repeating: 0, count: 26)
    for char in p {
        pDict[Int(char.asciiValue!) - 97] += 1
    }

    var s = Array(s)
    var answer = [Int]()
    var sDict = Array(repeating: 0, count: 26)
    for i in stride(from: 0, to: p.count, by: 1) {
        sDict[Int(s[i].asciiValue!) - 97] += 1
    }
    if isAnagram(sDict, pDict) {
        answer.append(0)
    }
    for i in stride(from: 0, to: s.count - p.count, by: 1) {
        sDict[Int(s[i].asciiValue!) - 97] -= 1
        sDict[Int(s[i+p.count].asciiValue!) - 97] += 1
        if isAnagram(sDict, pDict) {
            answer.append(i+1)
        }
    }
    return answer
}

private func isAnagram(_ s: [Int], _ p: [Int]) -> Bool {
    for i in stride(from: 0, to: 26, by: 1) {
        if s[i] != p[i] {
            return false
        }
    }
    return true
}