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Given a string and an integer k, you need to reverse the first k characters for every 2k characters counting from the start of the string. If there are less than k characters left, reverse all of them. If there are less than 2k but greater than or equal to k characters, then reverse the first k characters and left the other as original.
Example:
Input: s = "abcdefg", k = 2 Output: "bacdfeg"
Restrictions:
- The string consists of lower English letters only.
- Length of the given string and k will in the range [1, 10000]
给定一个字符串和一个整数 k，你需要对从字符串开头算起的每个 2k 个字符的前k个字符进行反转。如果剩余少于 k 个字符，则将剩余的所有全部反转。如果有小于 2k 但大于或等于 k 个字符，则反转前 k 个字符，并将剩余的字符保持原样。
示例:
输入: s = "abcdefg", k = 2 输出: "bacdfeg"
要求:
- 该字符串只包含小写的英文字母。
- 给定字符串的长度和 k 在[1, 10000]范围内。
308ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 var arr:[String] = [String]() 4 //将字符串的字符存入数组中 5 for char in s.characters 6 { 7 arr.append(String(char)) 8 } 9 for i in stride(from: 0,to: s.count ,by: 2 * k) 10 { 11 var num:Int = min(i + k - 1,s.count - 1) 12 for (index, value) in arr[i...num].reversed().enumerated() 13 { 14 arr[i + index] = value 15 } 16 } 17 //数组转换为字符串 18 return arr.reduce("", {$0 + $1}) 19 } 20 }
32ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 var arr = Array(s.characters) 4 var index = 0 5 6 while index < arr.count { 7 reverse(&arr, index, min(index + k - 1, arr.count - 1)) 8 index += 2 * k 9 } 10 return String(arr) 11 } 12 13 func reverse(_ arr: inout [Character], _ startIndex: Int, _ endIndex: Int) { 14 var start = startIndex 15 var end = endIndex 16 while start <= (startIndex + endIndex) / 2 { 17 (arr[start], arr[end]) = (arr[end], arr[start]) 18 start += 1 19 end -= 1 20 } 21 } 22 }
36ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 if k == 0 { 4 return s 5 } 6 let count = s.count 7 let time = count/(2*k) 8 let left = count%(2*k) 9 10 var array = [String]() 11 for i in 0..<time { 12 array.append(String(s.suffix(count-2*k*i).prefix(k*2))) 13 } 14 15 var result = "" 16 for str in array { 17 result += String(str.prefix(k).reversed()+str.suffix(k)) 18 } 19 20 let leftStr = s.suffix(left) 21 let leftReversed = leftStr.prefix(k).reversed() 22 let leftUnreversed = leftStr.suffix(leftStr.count-leftReversed.count) 23 24 result += leftReversed+leftUnreversed 25 return result 26 } 27 }
40ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 var chars = s.map { $0 } 4 5 var x = 0 6 while x < chars.count { 7 let rem = chars.count - x 8 if rem >= 2*k { 9 var curr = x 10 var max = x + k - 1 11 for _ in 0..<k/2 { 12 chars.swapAt(curr, max) 13 curr += 1 14 max -= 1 15 } 16 x += 2*k 17 } else if rem < k { 18 var curr = x 19 var max = chars.count-1 20 for _ in 0..<rem/2 { 21 chars.swapAt(curr, max) 22 curr += 1 23 max -= 1 24 } 25 break 26 } else { 27 var curr = x 28 var max = x + k - 1 29 for _ in 0..<k/2 { 30 chars.swapAt(curr, max) 31 curr += 1 32 max -= 1 33 } 34 break 35 } 36 } 37 38 return String(chars) 39 } 40 }
80ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 if s.count <= k { return String(s.reversed())} 4 var array = s.map{ String($0) } 5 var start = 0 6 var i = 0 7 while i < array.count { 8 reverse(in: &array, from:i, to:i+k) 9 i += 2*k 10 } 11 return array.reduce("", +) 12 } 13 14 func reverse(in array: inout [String], from: Int, to: Int) { 15 var start = from 16 var end = min(to, array.count) - 1 17 while start < end { 18 let tmp = array[start] 19 array[start] = array[end] 20 array[end] = tmp 21 22 start += 1 23 end -= 1 24 } 25 } 26 }
84ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 var array = s.map{ String($0) } 4 var start = 0 5 var i = 0 6 while i < array.count { 7 reverse(in: &array, from:i, to:i+k) 8 i += 2*k 9 } 10 return array.reduce("", +) 11 } 12 13 func reverse(in array: inout [String], from: Int, to: Int) { 14 var start = from 15 var end = min(to, array.count) - 1 16 while start < end { 17 let tmp = array[start] 18 array[start] = array[end] 19 array[end] = tmp 20 21 start += 1 22 end -= 1 23 } 24 } 25 }
92ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 4 var result = [String]() 5 var array = s.map{ String($0) } 6 var start = 0 7 var i = 0 8 while i < array.count { 9 if i == start { 10 var end = start+k >= array.count ? array.count : start+k 11 var slice = array[start...end-1] 12 result += Array(slice.reversed()) 13 start+=2*k 14 } else { 15 result.append(contentsOf: array[i ..< min(i+k, array.count)]) 16 } 17 i += k 18 } 19 return result.reduce("", +) 20 } 21 }
96ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 4 var result = [String]() 5 var array = s.map{ String($0) } 6 var start = 0 7 var i = 0 8 while i < array.count { 9 if i == start { 10 var end = start+k >= array.count ? array.count : start+k 11 var slice = array[start...end-1] 12 result += Array(slice.reversed()) 13 start+=2*k 14 } else { 15 var j = i 16 while j<min(i+k, array.count) { 17 result.append(array[j]) 18 j += 1 19 } 20 } 21 i += k 22 } 23 return result.reduce("", +) 24 } 25 }
100ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 var array = s.map{ String($0) } 4 var start = 0 5 var i = 0 6 while i < array.count { 7 reverse(in: &array, from:i, to:i+k) 8 i += 2*k 9 } 10 return array.reduce("", +) 11 } 12 13 func reverse(in array: inout [String], from: Int, to: Int) { 14 var start = from 15 var end = min(to, array.count) - 1 16 while start < end { 17 let tmp = array[start] 18 array[start] = array[end] 19 array[end] = tmp 20 21 start += 1 22 end -= 1 23 } 24 } 25 }
116ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 if k == 1 { 4 return s 5 } 6 if s.count <= k { 7 return String(s.reversed()) 8 } 9 var chars = Array(s) 10 var i = 0 11 while i * k < s.count { 12 if i % 2 == 0 { 13 if (i + 1) * k > s.count { 14 let end = s.count - i * k - 1 15 for ii in 0 ... (end / 2) { 16 let left = i * k + ii 17 let right = i * k + end - ii 18 let tmp = chars[left] 19 chars[left] = chars[right] 20 chars[right] = tmp 21 } 22 } else { 23 for ii in 0 ... (k / 2 - 1) { 24 let left = i * k + ii 25 let right = i * k + k - ii - 1 26 let tmp = chars[left] 27 chars[left] = chars[right] 28 chars[right] = tmp 29 } 30 } 31 32 } 33 i += 1 34 } 35 return String(chars) 36 } 37 }
136ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 4 var result = [String]() 5 var array = s.map{ String($0) } 6 var start = 0 7 var i = 0 8 while i < array.count { 9 if i == start { 10 var end = start+k >= array.count ? array.count : start+k 11 var slice = array[start...end-1] 12 result += Array(slice.reversed()) 13 start+=2*k 14 } else { 15 result.append(contentsOf: array[i ..< min(i+k, array.count)]) 16 } 17 i += k 18 } 19 return result.reduce("", +) 20 } 21 }
256ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 var reverseIndex = true 4 var index = 0 5 var newStr = "" 6 while(index < s.count - k) { 7 let range = s.index(s.startIndex, offsetBy: index)..<s.index(s.startIndex, offsetBy: index + k) 8 let substr = String(s[range]) 9 newStr += reverseIndex ? reverse(substr) : substr 10 11 reverseIndex = !reverseIndex 12 index += k 13 } 14 15 let range = s.index(s.startIndex, offsetBy: index)..<s.endIndex 16 let substr = String(s[range]) 17 newStr += reverseIndex ? reverse(substr) : substr 18 19 return newStr 20 } 21 22 func reverse(_ str: String) -> String { 23 var strArr = Array(str) 24 let count = strArr.count 25 guard count > 1 else { return str } 26 var index = 0 27 while(index < count / 2) { 28 let temp = strArr[count - 1 - index] 29 strArr[count - 1 - index] = strArr[index] 30 strArr[index] = temp 31 index += 1 32 } 33 return strArr.map { String(describing: $0) }.joined() 34 35 36 } 37 }
296ms
1 class Solution { 2 func reverseStr(_ s: String, _ k: Int) -> String { 3 var str = Array(s) 4 var i = 0 5 while(i < s.count) { 6 var start = i, end = min(i + k, s.count) - 1 7 while(start < end) { 8 let temp = str[end] 9 str[end] = str[start] 10 str[start] = temp 11 start += 1 12 end -= 1 13 } 14 i += 2 * k 15 } 16 return str.map{ String(describing: $0)}.joined() 17 } 18 }