Valid Palindrome Problem
Description
LeetCode Problem 125.
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:
1
2
3
Input: s = "A man, a plan, a canal: Panama"
Output: true
Explanation: "amanaplanacanalpanama" is a palindrome.
Example 2:
1
2
3
Input: s = "race a car"
Output: false
Explanation: "raceacar" is not a palindrome.
Example 3:
1
2
3
4
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.
Sample C++ Code
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
bool isPalindrome(string s) {
for (int i = 0, j = s.size() - 1; i < j; i++, j--) {
// Move 2 pointers from each end until they collide
while (!isalnum(s[i]) && i < j)
// Increment left pointer if not alphanumeric
i++;
while (!isalnum(s[j]) == false && i < j)
// Decrement right pointer if no alphanumeric
j--;
if (toupper(s[i]) != toupper(s[j]))
// Exit and return error if not match
return false;
}
return true;
}