LeetCode-in-Go
125. Valid Palindrome
Easy
A phrase is a palindrome if, after converting all uppercase letters into lowercase letters and removing all non-alphanumeric characters, it reads the same forward and backward. Alphanumeric characters include letters and numbers.
Given a string s, return true if it is a palindrome, or false otherwise.
Example 1:
Input: s = “A man, a plan, a canal: Panama”
Output: true
Explanation: “amanaplanacanalpanama” is a palindrome.
Example 2:
Input: s = “race a car”
Output: false
Explanation: “raceacar” is not a palindrome.
Example 3:
Input: s = “ “
Output: true
Explanation: s is an empty string “” after removing non-alphanumeric characters. Since an empty string reads the same forward and backward, it is a palindrome.
Constraints:
1 <= s.length <= 2 * 105sconsists only of printable ASCII characters.
Solution
func isPalindrome(s string) bool {
i := 0
j := len(s) - 1
res := true
for res {
for i < j && isNotAlphaNumeric(s[i]) {
i++
}
for i < j && isNotAlphaNumeric(s[j]) {
j--
}
if i >= j {
break
}
left := upperToLower(s[i])
right := upperToLower(s[j])
if left != right {
res = false
}
i++
j--
}
return res
}
func isNotAlphaNumeric(c byte) bool {
return (c < 'a' || c > 'z') && (c < 'A' || c > 'Z') && (c < '0' || c > '9')
}
func isUpper(c byte) bool {
return c >= 'A' && c <= 'Z'
}
func upperToLower(c byte) byte {
if isUpper(c) {
c += 32
}
return c
}