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 * 105s consists only of printable ASCII characters.class Solution {
public:
bool isAlpha(char c){
return ('A'<=c<='Z'||'a'<=c<='z');
}
bool isPalindrome(string s) {
int lt=0, rt=s.size()-1;
while(lt<rt){
while(!iswalnum(s[lt]) && lt<rt)
lt++;
while(!iswalnum(s[rt]) && lt<rt)
rt--;
if(tolower(s[lt])!=tolower(s[rt]))
return false;
lt++, rt--;
}
return true;
}
};class Solution {
public:
bool isPalindrome(string s) {
int lt=0, rt=s.size()-1;
while(lt<rt){
while(lt<rt && !iswalnum(s[lt]))
lt++;
while(lt<rt && !iswalnum(s[rt]))
rt--;
if(tolower(s[lt++])!=tolower(s[rt--]))
return false;
}
return true;
}
};class Solution {
public boolean isPalindrome(String s) {
s = s.toLowerCase();
return solve(s, 0, s.length() - 1);
}
private boolean solve(String s, int lt, int rt) {
while (lt < rt && !isAlphanumeric(s.charAt(lt)))
lt++;
while (lt < rt && !isAlphanumeric(s.charAt(rt)))
rt--;
if (lt < rt) {
System.out.println(s.charAt(lt) + "\t" + s.charAt(rt));
if (s.charAt(lt) != s.charAt(rt))
return false;
return solve(s, lt + 1, rt - 1);
}
return true;
}
private boolean isAlphanumeric(char c) {
return (c >= '0' && c <= '9') || (c >= 'a' && c <= 'z');
}
}