[Swift]LeetCode1209. 删除字符串中的所有相邻重复项 II | Remove All Adjacent Duplicates in String II

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Given a string s, a k duplicate removal consists of choosing k adjacent and equal letters from s and removing them causing the left and the right side of the deleted substring to concatenate together.

We repeatedly make k duplicate removals on s until we no longer can.

Return the final string after all such duplicate removals have been made.

It is guaranteed that the answer is unique.

Example 1:

Input: s = "abcd", k = 2
Output: "abcd"
Explanation: There's nothing to delete.

Example 2:

Input: s = "deeedbbcccbdaa", k = 3
Output: "aa"
Explanation: 
First delete "eee" and "ccc", get "ddbbbdaa"
Then delete "bbb", get "dddaa"
Finally delete "ddd", get "aa"

Example 3:

Input: s = "pbbcggttciiippooaais", k = 2
Output: "ps"

Constraints:

• 1 <= s.length <= 10^5
• 2 <= k <= 10^4
• s only contains lower case English letters.

---

给你一个字符串 s，「k 倍重复项删除操作」将会从 s 中选择 k 个相邻且相等的字母，并删除它们，使被删去的字符串的左侧和右侧连在一起。

你需要对 s 重复进行无限次这样的删除操作，直到无法继续为止。

在执行完所有删除操作后，返回最终得到的字符串。

本题答案保证唯一。

示例 1：

输入：s = "abcd", k = 2
输出："abcd"
解释：没有要删除的内容。

示例 2：

输入：s = "deeedbbcccbdaa", k = 3
输出："aa"
解释： 
先删除 "eee" 和 "ccc"，得到 "ddbbbdaa"
再删除 "bbb"，得到 "dddaa"
最后删除 "ddd"，得到 "aa"

示例 3：

输入：s = "pbbcggttciiippooaais", k = 2
输出："ps"

提示：

• 1 <= s.length <= 10^5
• 2 <= k <= 10^4
• s 中只含有小写英文字母。

---

Runtime: 84 ms

Memory Usage: 21.5 MB

class Solution {
    func removeDuplicates(_ s: String, _ k: Int) -> String {
        var st:[Character] = [Character]()
        var cnt:[Int] = [Int]()
        for c in s
        {
            if st.count > 0 && st.last! == c
            {
                cnt[cnt.count - 1] += 1
            }
            else
            {
                st.append(c)
                cnt.append(1)
            }
            while(st.count > 0 && cnt.last! == k)
            {
                st.removeLast()
                cnt.removeLast()
            }
        }
        var ret:String = String()
        for i in 0..<st.count
        {
            ret += String(repeating:st[i],count:cnt[i])
        }
        return ret
    }
} 

---

32ms

class Solution {
    func removeDuplicates(_ s: String, _ k: Int) -> String {
               
        if k <= 1 {
            return ""
        }
        if s.count < 1 {
            return s
        }
        var chars = Array(s)

        func remove(_ chars: inout [Character]) {
            if chars.count < k {
                return
            }

            var ct = 1
            var idx = -1
            for i in 1..<chars.count {
                if chars[i] == chars[i-1] {
                    ct += 1
                } else {
                    ct = 1
                }

                if ct >= k {
                    idx = i
                    break
                }
            }

            if idx != -1 {
                chars.removeSubrange(idx-k+1...idx)
                // print(chars)
                remove(&chars)
            }
        }
        remove(&chars)
        return String(chars)
    }
}

---

36ms

class Solution {
    func removeDuplicates(_ s: String, _ k: Int) -> String {
        var stack = [Character]()
        var count = 1
        for c in s {
            stack.append(c)
            
            if stack.count > 1 {
                if stack[stack.count - 1] == stack[stack.count - 2] {
                    count += 1
                    if count == k {
                        stack.removeLast(k)
                        if !stack.isEmpty {
                            count = 0
                            var i = stack.count - 1
                            let last = stack[i]
                            while i >= 0, stack[i] == last {
                                count += 1
                                i -= 1
                            }
                        } else {
                            count = 1
                        }
                    }
                } else {
                    count = 1
                }
            }
        }
        
        return String(stack)
    }
}

---

40ms

class Solution {
    func removeDuplicates(_ s: String, _ k: Int) -> String {
        
        guard k > 1 else { return "" }
        var stack = Array(s)
        
        var arr = [Int](repeating: 0, count: s.count)
        
        var end = 0
        for c in s {
            stack[end] = c
            if end == 0 {
                arr[end] = 1
            } else if stack[end] == stack[end-1] {
                arr[end] = arr[end-1] + 1
            } else {
                arr[end] = 1
            }
            
            while end + 1 >= k && arr[end] == k {
                end = end + 1 - k - 1
            }
            end += 1
        }
        return String(stack[0..<end])
    }
}

---

56ms

class Solution {
    func removeDuplicates(_ s: String, _ k: Int) -> String {
        var stack: [(character: Character, count: Int)] = []
        
        for c in s {
            guard let last = stack.last, last.character == c else {
                stack.append((c, 1))
                continue
            }
            
            if last.count == k - 1 {
                _ = stack.removeLast()
            } else {
                stack[stack.count - 1] = (c, last.count + 1)
            }
        }
        
        var ans: String = ""
        for value in stack {
            ans.append(contentsOf: String(repeating: value.character, count: value.count))
        }
        
        return ans
    }
}