[Swift]LeetCode680. 验证回文字符串 Ⅱ | Valid Palindrome II

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Given a non-empty string s, you may delete at most one character. Judge whether you can make it a palindrome.

Example 1:

Input: "aba"
Output: True 

Example 2:

Input: "abca"
Output: True
Explanation: You could delete the character 'c'. 

Note:

1. The string will only contain lowercase characters a-z. The maximum length of the string is 50000.

---

给定一个非空字符串 s，最多删除一个字符。判断是否能成为回文字符串。

示例 1:

输入: "aba"
输出: True

示例 2:

输入: "abca"
输出: True
解释: 你可以删除c字符。

注意:

1. 字符串只包含从 a-z 的小写字母。字符串的最大长度是50000。

---

196ms

class Solution {
    func validPalindrome(_ s: String) -> Bool {
        let chars = Array(s.lowercased().unicodeScalars)
        
        var start = 0
        var end = chars.count - 1
        
        while start < end {
            if chars[start] != chars[end] {
                return validPalindromeRange(chars, i: start + 1, j: end) || validPalindromeRange(chars, i: start, j: end - 1)
            }
            
            start += 1
            end -= 1
        }
        
        return true
    }
    
    func validPalindromeRange(_ chars: [Unicode.Scalar], i: Int, j: Int) -> Bool {
        var start = i
        var end = j
        
        while start < end {
            if chars[start] != chars[end] { return false }
            start += 1
            end -= 1
        }
        return true
    }
}

---

200ms

class Solution {
    func validPalindrome(_ s: String) -> Bool {
        let array = Array(s)
        return isPalindrome(array, 0, array.count - 1)
    }
    
    fileprivate func isPalindrome(_ array: [Character], _ i: Int, _ j: Int, alreadyRemoved: Bool = false) -> Bool {
        var i = i, j = j
        while i < j {
            if array[i] != array[j] {
                if alreadyRemoved {
                    return false
                } else {
                    return isPalindrome(array, i + 1, j, alreadyRemoved: true) || 
                           isPalindrome(array, i, j - 1, alreadyRemoved: true)
                }
            } else {
                i += 1
                j -= 1
            }
        }
        return true
    }
}

---

204ms

class Solution {
    func validPalindrome(_ s: String) -> Bool {

        var s = Array(s)
        var i = 0, j = s.count - 1

        while i < j {
            if s[i] == s[j] {
                i += 1
                j -= 1
            } else {
                return isValid(s, i, j - 1) || isValid(s, i + 1, j)
            }
        }

        return true
    }

    func isValid(_ s: [Character], _ i: Int, _ j: Int) -> Bool {

        let mid = (i + j) / 2

        for k in i...mid {
            if s[k] != s[j - (k - i)] {
                return false
            }
        }
        return true
    }
}

---

Runtime: 224 ms

Memory Usage: 20.1 MB

class Solution {
    func validPalindrome(_ s: String) -> Bool {
        var arr:[Character] = Array(s)
        var left:Int = 0
        var right:Int = arr.count - 1
        while (left < right)
        {
            if arr[left] != arr[right]
            {
                 return isValid(arr, left, right - 1) || isValid(arr, left + 1, right)
            }
            left += 1
            right -= 1
        }
        return true
    }
    
    func isValid(_ arr:[Character],_ left:Int,_ right:Int) -> Bool
    {
        var left = left
        var right = right
        while (left < right)
        {
            if arr[left] != arr[right]
            {
                return false
            }
            left += 1
            right -= 1
        }
        return true
    }
}

---

232ms

class Solution {
    func validPalindrome(_ s: String) -> Bool {
        let stringArray = Array(s.utf16)
        if stringArray.count == 1 || stringArray.count == 2 {return true}
        var i = 0
        var j = stringArray.count - 1
        var alreadyRemoved = false
        
        while i < j {
            if stringArray[i] != stringArray[j] { 
                if alreadyRemoved {return false}
                
                if i+2 < j-1, stringArray[i+1] == stringArray[j],
                stringArray[i+2] == stringArray[j-1] {
                    i += 1
                    alreadyRemoved = true
                } else if i+2 >= j-1, stringArray[i+1] == stringArray[j] {
                    i += 1
                    alreadyRemoved = true
                } else if stringArray[i] == stringArray[j-1], stringArray[i+1] == stringArray[j-2] {
                    j -= 1
                    alreadyRemoved = true
                } else {
                    return false
                }
                
                
            }
            i += 1
            j -= 1        
        }            
        return true
    }
}

---

244ms

class Solution {
    func validPalindrome(_ s: String) -> Bool {
        return s.isPalindrome
    }
}

extension String {
    
    var isPalindrome: Bool {
        let array = Array(self)
        return isPalindrome(array, 0, array.count-1)
    }
    
    private func isPalindrome(_ array: [Character], _ i: Int, _ j: Int, _ isAlreadyMismatched: Bool = false) -> Bool {
        var left = i, right = j
        while left < right {
            if array[left] != array[right] {
                return isAlreadyMismatched ? false : (isPalindrome(array, left, right-1, true) || isPalindrome(array, left+1, right, true))
            }
            
            left+=1
            right-=1
        }
        
        return true
    }
}