[Swift]LeetCode1156. 单字符重复子串的最大长度 | Swap For Maximum Repeated Substring

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A string is a repeated character string if all characters in that string are the same.  For example, "cccc" is a repeated character string.

Return the largest L such that: after either swapping two characters in text or doing nothing, there exists a repeated character substring of text with length L.

Example 1:

Input: text = "ababa"
Output: 3

Example 2:

Input: text = "aaabaaa"
Output: 6

Example 3:

Input: text = "aaabbaaa"
Output: 4

Example 4:

Input: text = "aaaaa"
Output: 5

Example 5:

Input: text = "abcdef"
Output: 1 

Constraints:

• 1 <= text.length <= 20000
• text consist of lowercase English characters only.

---

如果字符串中的所有字符都相同，那么这个字符串是单字符重复的字符串。

给你一个字符串 text，你只能交换其中两个字符一次或者什么都不做，然后得到一些单字符重复的子串。返回其中最长的子串的长度。

示例 1：

输入：text = "ababa"
输出：3

示例 2：

输入：text = "aaabaaa"
输出：6

示例 3：

输入：text = "aaabbaaa"
输出：4

示例 4：

输入：text = "aaaaa"
输出：5

示例 5：

输入：text = "abcdef"
输出：1 

提示：

• 1 <= text.length <= 20000
• text 仅由小写英文字母组成。

---

56ms

class Solution {
    func maxRepOpt1(_ text: String) -> Int {
        let chars = Array(text)
        var idxdic = [Character: [Int]]()
        for i in chars.indices {
            let c = chars[i]
            var arr = idxdic[c, default: [Int]()]
            arr.append(i)
            idxdic[c] = arr
        }
        var ans = 0
        for (_, arr) in idxdic {
            ans = max(ans, lenthOfArr(arr))
        }
        return ans
    }

    func lenthOfArr(_ arr: [Int]) -> Int {
        if arr.count == 0 { return 0 }
        var tuples = [(Int, Int)]()
        var curStar = arr[0]
        var curEnd = arr[0]
        for i in 1..<arr.count {
            if arr[i]-curEnd == 1 {
                curEnd = arr[i]
            } else {
                tuples.append((curStar, curEnd))
                curStar = arr[i]
                curEnd = arr[i]
            }
        }
        tuples.append((curStar, curEnd))
        var tuplefirst = tuples[0]
        var ans = tuplefirst.1 - tuplefirst.0 + 1
        for i in 1..<tuples.count {
            let curTuple = tuples[i]
            if curTuple.0 - tuplefirst.1 == 2 {
                let lastLen = tuplefirst.1 - tuplefirst.0 + 1
                let curLen = curTuple.1 - curTuple.0 + 1
                ans = max(ans, lastLen+curLen)
                if i != tuples.count - 1 || i > 1 {
                    ans = max(ans, lastLen+curLen+1)   
                } 
            } else {
                let curLen = curTuple.1 - curTuple.0 + 1
                let lastLen = tuplefirst.1 - tuplefirst.0 + 1
                ans = max(ans, lastLen+1) 
                ans = max(ans, curLen+1)
            }
            tuplefirst = curTuple
        }
        return ans
    }
}

---

120ms

class Solution {
    func maxRepOpt1(_ text: String) -> Int {
        let characters = Array(text)
        var result = 0
        var hash = [Character:[Int]]()
        
        for (index, character) in characters.enumerated() {
            hash[character] = (hash[character] ?? []) + [index]
        }
        
        for (key, value) in hash {
            var consecutiveCount = 1, previousConsecutiveCount = 0, maximum = 0
            var i = 1
            
            while i < value.count {
                if value[i] == value[i-1] + 1 { consecutiveCount += 1 }
                else {
                    previousConsecutiveCount = value[i] == value[i-1] + 2 ? consecutiveCount : 0
                    consecutiveCount = 1
                }
                maximum = max(maximum, consecutiveCount + previousConsecutiveCount)
                i += 1
            }
            
            maximum = max(maximum, consecutiveCount + previousConsecutiveCount)
            result = max(result, maximum + (value.count > maximum ? 1 : 0))
        }
        
        return result
    }
}

---

Runtime: 144 ms

Memory Usage: 21.7 MB

class Solution {
    func maxRepOpt1(_ text: String) -> Int {
        let arrT:[Character] = Array(text)
        let n:Int = text.count
        var best:Int = 0
        let alphabet:[Character] = ["a","b","c","d","e","f","g","h","i","j","k","l","m","n","o","p","q","r","s","t","u","v","w","x","y","z"]
        for c in alphabet
        {
            var count:Int = 0
            for i in 0..<n
            {
                if arrT[i] == c
                {
                    count += 1
                }
            }
            if count == n
            {
                best = n
                continue
            }
            for i in 0..<n
            {
                if arrT[i] != c
                {
                    var left:Int = i
                    var right:Int = i
                    while (left > 0 && arrT[left - 1] == c)
                    {
                        left -= 1
                    }
                    while (right < n - 1 && arrT[right + 1] == c)
                    {
                        right += 1
                    }
                    var combined:Int = right - left
                    if combined == count
                    {
                        best = max(best, count)
                    }
                    else
                    {
                        best = max(best, combined + 1)
                    }
                }
            }
        }
        return best        
    }
}