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Difficulty Level: Easy
1. Description
Given a string, verify that it is a palindrome, considering only alphanumeric characters, ignoring case of letters.
Explanation: In this problem, we define the empty string as a valid palindrome.
2. Example
Example 1
输入: "A man, a plan, a canal: Panama"
输出: true
解释："amanaplanacanalpanama" 是回文串
Example 2
输入: "race a car"
输出: false
解释："raceacar" 不是回文串
Restrictions:
1 <= s.length <= 2 * 10^5- string
sconsisting of ASCII characters
3. Answers
class ValidPalindrome {
func isPalindrome(_ s: String) -> Bool {
var i = 0, j = s.count - 1
let sChars = Array(s.lowercased())
while i < j {
while !sChars[i].isAlphanumeric && i < j {
i += 1
}
while !sChars[j].isAlphanumeric && i < j {
j -= 1
}
if sChars[i] != sChars[j] {
return false
} else {
i += 1
j -= 1
}
}
return true
}
}
extension Character {
var isValid: Bool {
return isLetter || isNumber
}
}
- Main idea: For each index in the first half of the String, compare the two values at the mirror index. .
- Time Complexity: O(n)
- Space Complexity: O(n)
Repository for the algorithm solution: LeetCode-Swift
Click to go to LeetCode practice
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