Algorithm
Problem Nmae: 125. Valid Palindrome
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.
Code Examples
#1 Code Example with C Programming
Code -
C Programming
bool isPalindrome(char* s) {
int i = 0;
int j;
char a, b;
if (!s || !*s) return true;
j = strlen(s) - 1;
while (i < j) {
a = s[i];
b = s[j];
if (!((a >= '0' && a < = '9') ||
(a >= 'A' && a <= 'Z') ||
(a >= 'a' && a <= 'z'))) {
i ++;
continue;
}
if (!((b >= '0' && b < = '9') ||
(b >= 'A' && b <= 'Z') ||
(b >= 'a' && b <= 'z'))) {
j --;
continue;
}
a = a > 'Z' ? a - 'a' + 'A' : a;
b = b > 'Z' ? b - 'a' + 'A' : b;
if (a != b) {
return false;
}
i ++;
j --;
}
return true;
}
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Output
#2 Code Example with C++ Programming
Code -
C++ Programming
class Solution {
public:
bool isPalindrome(string s) {
int i = 0, j = s.size() - 1;
while(i < j){
while(i < j && !isalnum(s[i])) i++;
while(i < j && !isalnum(s[j])) j--;
if(tolower(s[i++]) != tolower(s[j--])) return false;
}
return true;
}
};
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Output
#3 Code Example with Java Programming
Code -
Java Programming
class Solution {
public boolean isPalindrome(String s) {
int startIdx = 0;
int endIdx = s.length() - 1;
while (startIdx < endIdx) {
if (!isAlphanumeric(s.charAt(startIdx))) {
startIdx++;
} else if (!isAlphanumeric(s.charAt(endIdx))) {
endIdx--;
} else {
if (!areSame(s.charAt(startIdx), s.charAt(endIdx))) {
return false;
}
startIdx++;
endIdx--;
}
}
return true;
}
private boolean areSame(char c1, char c2) {
if (Character.isAlphabetic(c1) && Character.isAlphabetic(c2)) {
return Character.toLowerCase(c1) == Character.toLowerCase(c2);
} else if (Character.isDigit(c1) && Character.isDigit(c2)) {
return c1 == c2;
} else {
return false;
}
}
private boolean isAlphanumeric(char c) {
return Character.isAlphabetic(c) || Character.isDigit(c);
}
}
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Output
#4 Code Example with Javascript Programming
Code -
Javascript Programming
const isPalindrome = function(s) {
let start = 0
let end = s.length - 1
while(start < end) {
while(start < s.length && !valid(s[start])) {
start++
}
while(end >=0 && !valid(s[end])) {
end--
}
if(start < s.length && end >=0) {
if(s[start].toLowerCase() !== s[end].toLowerCase()) return false
}
start++
end--
}
return true
};
function valid(c) {
const code = c.toLowerCase().charCodeAt(0)
const zeroCode = ('0').charCodeAt(0)
const nineCode = ('9').charCodeAt(0)
const aCode = ('a').charCodeAt(0)
const zCode = ('z').charCodeAt(0)
if( (code >= zeroCode && code <= nineCode> || ( code >= aCode && code <= zCode ) ) return true
return false
}
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Output
#5 Code Example with Python Programming
Code -
Python Programming
class Solution:
def isPalindrome(self, s):
"""
:type s: str
:rtype: bool
"""
import string
return True if s=="" or [i.lower() for i in s if i in string.digits or i in string.ascii_letters]==[i.lower() for i in s if i in string.digits or i in string.ascii_letters][::-1] else False
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Output
#6 Code Example with C# Programming
Code -
C# Programming
namespace LeetCode
{
public class _0125_ValidPalindrome
{
public bool IsPalindrome(string s)
{
if (string.IsNullOrWhiteSpace(s)) return true;
s = s.ToLower();
int head = 0, tail = s.Length - 1;
while (head < = tail)
{
if ((s[head] < 'a' || s[head] > 'z') && (s[head] < '0' || s[head] > '9'))
head++;
else if ((s[tail] < 'a' || s[tail] > 'z') && (s[tail] < '0' || s[tail] > '9'))
tail--;
else if (s[head] != s[tail])
return false;
else
{
head++;
tail--;
}
}
return true;
}
}
}
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Output