125. Valid Palindrome

Difficulty: Easy

Topics

• Strings
• Two Pointers

Problem Statement

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.

Examples

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 * 10^5
• s consists only of printable ASCII characters.

Solution

func isPalindrome(s string) bool {
	var b []rune
	for _, v := range s {
		if (v >= 'a' && v <= 'z') || (v >= '0' && v <= '9') {
			b = append(b, v)
		} else if v >= 'A' && v <= 'Z' {
			b = append(b, v+32)
		}
	}

	l, r := 0, len(b)-1
	for l <= r {
		if b[l] != b[r] {
			return false
		}
		l++
		r--
	}
	return true
}