运行时速度差异，而属性名称的差异相同

Question

当我声明let属性与方法参数相同时， 运行速度为72毫秒（测试10多次试验）。

如果我声明为差异名称，则运行速度为48xx毫秒。 （测试10多个试验）

有人可以告诉我发生了什么事吗？ 谢谢。

密码问题： https://leetcode.com/problems/find-all-anagrams-in-a-string/submissions/

/*
Time Submitted Status Runtime Memory Language
a few seconds ago   Accepted    72 ms   22.2 MB swift
*/

class Solution {
    func findAnagrams(_ s: String, _ p: String) -> [Int] {
        var result = [Int]()
        var ref = Array<Int>(repeating: 0, count: 26)
        var map = ref

        let p = p.unicodeScalars
            .map{ $0.value - Unicode.Scalar("a").value }
            .map{ Int($0) }
        let s = s.unicodeScalars
            .map{ $0.value - Unicode.Scalar("a").value }
            .map{ Int($0) }

        p.forEach{ ref[$0] += 1 }

        for i in 0..<s.count {
            map[s[i]] += 1
            if i - p.count >= 0 {
                map[s[i-p.count]] -= 1
            }

            if map == ref {
                result.append(i - p.count + 1)
            }
        }
        return result
    }
}

/*
Time Submitted Status Runtime Memory Language
a few seconds ago   Accepted    4868 ms    22 MB    swift
*/

class Solution {
    func findAnagrams(_ s: String, _ p: String) -> [Int] {
        var result = [Int]()
        var ref = Array<Int>(repeating: 0, count: 26)
        var map = ref

        let pTest = p.unicodeScalars
            .map{ $0.value - Unicode.Scalar("a").value }
            .map{ Int($0) }
        let sTest = s.unicodeScalars
            .map{ $0.value - Unicode.Scalar("a").value }
            .map{ Int($0) }

        pTest.forEach{ ref[$0] += 1 }

        for i in 0..<s.count {
            map[sTest[i]] += 1
            if i - p.count >= 0 {
                map[sTest[i-p.count]] -= 1
            }

            if map == ref {
                result.append(i - p.count + 1)
            }
        }
        return result
    }
}