feat: add swift implementation to lcof2 problem: No.017 (#3005)

Author: klever34

lcof2/剑指 Offer II 017. 含有所有字符的最短字符串/README.md

@@ -326,6 +326,57 @@ func minWindow(s string, t string) string {
 }
 ```
 
+#### Swift
+
+```swift
+class Solution {
+    func minWindow(_ s: String, _ t: String) -> String {
+        let m = s.count, n = t.count
+        if n > m {
+            return ""
+        }
+
+        var need = [Character: Int]()
+        var window = [Character: Int]()
+
+        for ch in t {
+            need[ch, default: 0] += 1
+        }
+
+        let sArray = Array(s)
+        var start = 0, minLen = Int.max
+        var left = 0, right = 0
+
+        while right < m {
+            let ch = sArray[right]
+            window[ch, default: 0] += 1
+            right += 1
+
+            while check(need, window) {
+                if right - left < minLen {
+                    minLen = right - left
+                    start = left
+                }
+                let leftChar = sArray[left]
+                window[leftChar, default: 0] -= 1
+                left += 1
+            }
+        }
+
+        return minLen == Int.max ? "" : String(sArray[start..<start + minLen])
+    }
+
+    private func check(_ need: [Character: Int], _ window: [Character: Int]) -> Bool {
+        for (key, value) in need {
+            if window[key, default: 0] < value {
+                return false
+            }
+        }
+        return true
+    }
+}
+```
+
 <!-- tabs:end -->
 
 <!-- solution:end -->

lcof2/剑指 Offer II 017. 含有所有字符的最短字符串/Solution.swift

@@ -0,0 +1,46 @@
+class Solution {
+    func minWindow(_ s: String, _ t: String) -> String {
+        let m = s.count, n = t.count
+        if n > m {
+            return ""
+        }
+
+        var need = [Character: Int]()
+        var window = [Character: Int]()
+        
+        for ch in t {
+            need[ch, default: 0] += 1
+        }
+
+        let sArray = Array(s)
+        var start = 0, minLen = Int.max
+        var left = 0, right = 0
+
+        while right < m {
+            let ch = sArray[right]
+            window[ch, default: 0] += 1
+            right += 1
+            
+            while check(need, window) {
+                if right - left < minLen {
+                    minLen = right - left
+                    start = left
+                }
+                let leftChar = sArray[left]
+                window[leftChar, default: 0] -= 1
+                left += 1
+            }
+        }
+
+        return minLen == Int.max ? "" : String(sArray[start..<start + minLen])
+    }
+
+    private func check(_ need: [Character: Int], _ window: [Character: Int]) -> Bool {
+        for (key, value) in need {
+            if window[key, default: 0] < value {
+                return false
+            }
+        }
+        return true
+    }
+}