[Swift]LeetCode424. 替换后的最长重复字符 | Longest Repeating Character Replacement

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Given a string that consists of only uppercase English letters, you can replace any letter in the string with another letter at most k times. Find the length of a longest substring containing all repeating letters you can get after performing the above operations.

Note:
Both the string's length and k will not exceed 104.

Example 1:

Input:
s = "ABAB", k = 2

Output:
4

Explanation:
Replace the two 'A's with two 'B's or vice versa. 

Example 2:

Input:
s = "AABABBA", k = 1

Output:
4

Explanation:
Replace the one 'A' in the middle with 'B' and form "AABBBBA".
The substring "BBBB" has the longest repeating letters, which is 4.

---

给你一个仅由大写英文字母组成的字符串，你可以将任意位置上的字符替换成另外的字符，总共可最多替换 k 次。在执行上述操作后，找到包含重复字母的最长子串的长度。

注意:
字符串长度 和 k 不会超过 104。

示例 1:

输入:
s = "ABAB", k = 2

输出:
4

解释:
用两个'A'替换为两个'B',反之亦然。

示例 2:

输入:
s = "AABABBA", k = 1

输出:
4

解释:
将中间的一个'A'替换为'B',字符串变为 "AABBBBA"。
子串 "BBBB" 有最长重复字母, 答案为 4。

---

88ms

class Solution {
    func characterReplacement(_ s: String, _ k: Int) -> Int {
        var count: [Character: Int] = [:]
        let s = Array(s)
        let n = s.count
        var start = 0
        var end = 0
        var res = 0
        var maxCount = 0
        while end < n {
            count[s[end]] = (count[s[end]] ?? 0) + 1
            maxCount = max(maxCount, count[s[end]]!)
            while end - start + 1 - maxCount > k {
                count[s[start]] = count[s[start]]! - 1
                start += 1
            }
            res = max(res, end - start + 1)
            end += 1
        }
        return res
    }
}

---

280ms

class Solution {
    func characterReplacement(_ s: String, _ k: Int) -> Int {
      var slidingWindows = Array(repeating: 0, count: 26)
        var endIndex = 0
        var startIndex = 0
        var maxRepeatCount = 0
        var maxCount = 0
        let chats = s.utf8CString
        let count = chats.count - 1
        while endIndex < count{
            let currentIndex = Int(chats[endIndex] - 65)
            slidingWindows[currentIndex] += 1
            maxCount = max(maxCount, slidingWindows[currentIndex])
            if endIndex - startIndex + 1 - maxCount > k {
                slidingWindows[Int(chats[startIndex] - 65)] -= 1
                startIndex += 1
                slidingWindows.forEach { (element) in
                    if element > maxCount {
                        maxCount = element
                    }
                }
            }
            maxRepeatCount = max(maxRepeatCount, endIndex - startIndex + 1)
            endIndex += 1
        }
        return maxRepeatCount
    }
}

---

6792ms

class Solution {
    func characterReplacement(_ s: String, _ k: Int) -> Int {
        var res:Int = 0
        var maxCnt:Int = 0
        var start:Int = 0
        var counts:[Int] = [Int](repeating:0,count:26)
        //A:65
        for i in 0..<s.count
        {
            var num:Int = s[i].ascii - 65
            counts[num] += 1
            maxCnt = max(maxCnt,counts[num])
            while(i - start + 1 - maxCnt > k)
            {
                counts[s[start].ascii - 65] -= 1
                start += 1
            }
            res = max(res, i - start + 1)            
        }
        return res
    }
}

extension String {        
    //subscript函数可以检索数组中的值
    //直接按照索引方式截取指定索引的字符
    subscript (_ i: Int) -> Character {
        //读取字符
        get {return self[index(startIndex, offsetBy: i)]}
        
    }
}

extension Character  
{  
  //属性：ASCII整数值(定义小写为整数值)
   var ascii: Int {
        get {
            let s = String(self).unicodeScalars
            return Int(s[s.startIndex].value)
        }
    }
}