添加 1002. 查找常用字符 Swift版本

problems/1002.查找常用字符.md

@@ -268,6 +268,47 @@ func min(a,b int)int{
     return a
 }
 ```
+
+Swift：
+```swift
+func commonChars(_ words: [String]) -> [String] {
+    var res = [String]()
+    if words.count < 1 {
+        return res
+    }
+    let aUnicodeScalarValue = "a".unicodeScalars.first!.value
+    let lettersMaxCount = 26
+    // 用于统计所有字符串每个字母出现的 最小 频率
+    var hash = Array(repeating: 0, count: lettersMaxCount)
+    // 统计第一个字符串每个字母出现的次数
+    for unicodeScalar in words.first!.unicodeScalars {
+        hash[Int(unicodeScalar.value - aUnicodeScalarValue)] += 1
+    }
+    // 统计除第一个字符串每个字母出现的次数
+    for idx in 1 ..< words.count {
+        var hashOtherStr = Array(repeating: 0, count: lettersMaxCount)
+        for unicodeScalar in words[idx].unicodeScalars {
+            hashOtherStr[Int(unicodeScalar.value - aUnicodeScalarValue)] += 1
+        }
+        // 更新hash,保证hash里统计的字母为出现的最小频率
+        for k in 0 ..< lettersMaxCount {
+            hash[k] = min(hash[k], hashOtherStr[k])
+        }
+    }
+    // 将hash统计的字符次数，转成输出形式
+    for i in 0 ..< lettersMaxCount {
+        while hash[i] != 0 { // 注意这里是while，多个重复的字符
+            let currentUnicodeScalarValue: UInt32 = UInt32(i) + aUnicodeScalarValue
+            let currentUnicodeScalar: UnicodeScalar = UnicodeScalar(currentUnicodeScalarValue)!
+            let outputStr = String(currentUnicodeScalar) // UnicodeScalar -> String
+            res.append(outputStr)
+            hash[i] -= 1
+        }
+    }
+    return res
+}
+```
+
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