feat: add swift implementation to lcof2 problem: No.015 (doocs#3003)

Author: klever34

lcof2/剑指 Offer II 015. 字符串中的所有变位词/README.md

@@ -213,6 +213,51 @@ function findAnagrams(s: string, p: string): number[] {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func findAnagrams(_ s: String, _ p: String) -> [Int] {
+        let m = s.count
+        let n = p.count
+        var ans = [Int]()
+
+        if m < n {
+            return ans
+        }
+
+        var cnt1 = Array(repeating: 0, count: 26)
+        var cnt2 = Array(repeating: 0, count: 26)
+
+        let aAsciiValue = Character("a").asciiValue!
+
+        for i in 0..<n {
+            let sIdx = Int(s.utf8[s.utf8.index(s.utf8.startIndex, offsetBy: i)] - aAsciiValue)
+            let pIdx = Int(p.utf8[p.utf8.index(p.utf8.startIndex, offsetBy: i)] - aAsciiValue)
+            cnt1[sIdx] += 1
+            cnt2[pIdx] += 1
+        }
+
+        if cnt1 == cnt2 {
+            ans.append(0)
+        }
+
+        for i in n..<m {
+            let sIdxNew = Int(s.utf8[s.utf8.index(s.utf8.startIndex, offsetBy: i)] - aAsciiValue)
+            let sIdxOld = Int(s.utf8[s.utf8.index(s.utf8.startIndex, offsetBy: i - n)] - aAsciiValue)
+            cnt1[sIdxNew] += 1
+            cnt1[sIdxOld] -= 1
+
+            if cnt1 == cnt2 {
+                ans.append(i - n + 1)
+            }
+        }
+
+        return ans
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 015. 字符串中的所有变位词/Solution.swift

@@ -0,0 +1,40 @@
+class Solution {
+    func findAnagrams(_ s: String, _ p: String) -> [Int] {
+        let m = s.count
+        let n = p.count
+        var ans = [Int]()
+        
+        if m < n {
+            return ans
+        }
+        
+        var cnt1 = Array(repeating: 0, count: 26)
+        var cnt2 = Array(repeating: 0, count: 26)
+        
+        let aAsciiValue = Character("a").asciiValue!
+        
+        for i in 0..<n {
+            let sIdx = Int(s.utf8[s.utf8.index(s.utf8.startIndex, offsetBy: i)] - aAsciiValue)
+            let pIdx = Int(p.utf8[p.utf8.index(p.utf8.startIndex, offsetBy: i)] - aAsciiValue)
+            cnt1[sIdx] += 1
+            cnt2[pIdx] += 1
+        }
+        
+        if cnt1 == cnt2 {
+            ans.append(0)
+        }
+        
+        for i in n..<m {
+            let sIdxNew = Int(s.utf8[s.utf8.index(s.utf8.startIndex, offsetBy: i)] - aAsciiValue)
+            let sIdxOld = Int(s.utf8[s.utf8.index(s.utf8.startIndex, offsetBy: i - n)] - aAsciiValue)
+            cnt1[sIdxNew] += 1
+            cnt1[sIdxOld] -= 1
+            
+            if cnt1 == cnt2 {
+                ans.append(i - n + 1)
+            }
+        }
+        
+        return ans
+    }
+}