CareerCup

Time complexity O(n/2)

import java.util.*;
import java.io.*;

public class ispalindrome {
	public static boolean checkpalindrome(String str)
	{
		int n=str.length();
		boolean flag=true;
		for(int i=0;i<=n/2 && flag ==true;i++)
		{
			if(str.charAt(i) != str.charAt(n-i-1))
			{
				flag=false;
			}
		}
		return flag;
	}
	public static void main(String args[])
	{
		Scanner ip=new Scanner(System.in);
		String str = ip.nextLine();
		boolean flag = checkpalindrome(str);

		if(flag==true)
			System.out.print("palindrome");
		else
			System.out.println("Not a Palindrome");

	}

}

bool isPlaindrome(string str) {
	int n = str.length();
	for(int i = 0, j = n - 1; i < j; ++i, --j) {
		if(str[i] != str[j]) return false;
	}
        return true;
}

void panlindrome(String in){
        in = trim(in);
        for(int i=0, j=in.length()-1; i < j; i++, j--){
            if(in.charAt(i) != in.charAt(j)){
                System.out.println("False");
                return;
            }
        }
        System.out.println("True");
    }
    
    String trim(String in){
        in = in.toLowerCase();
        StringBuilder builder = new StringBuilder(in.trim().length());
        for(int i=0; i< in.length(); i++){
            char ch = in.charAt(i);
            if((ch >= 65 && ch <= 90) || (ch >= 97 && ch <= 122)){
                builder.append(ch);
            }
        }
        return builder.toString();
    }

public static boolean isPalindrome(String str) {
        int start = 0;
        int end = str.length() - 1;

        while (start < end) {
            if (str.charAt(start) != str.charAt(end)) {
                return false;
            }
            start++;
            end--;
        }

        return true;

}

/*
* compare ith char from 0 to i with (legnth -i)th char from length to length-i
* i = 0 to n/2 
* */
public boolean process(String s){
		char [] array = s.toCharArray();
		for(int i=0; i<(array.length)/2; i++){
			if(array[i] != array[array.length-i-1])
				return false;
		}
		
		return true;

void chkPalindrome(char strPalin[250])
{
	int len = strlen(strPalin);
	int j = len-1;
	for(int i=0;i<len/2;i++)
	{
		if(strPalin[i] == strPalin[j])
		{
			--j;
			continue;
		}
		else
		{
			cout << "not a palindrome";
			return;
		}
	}
	cout << "palindrome";
}

O(n) complexity and O(1) memory:

public static boolean isPalindrome(String str){
    //handle the invalid cases
    if(str == null){
        return false;
    }
    
    int lo = 0;
    int hi = str.length()-1;
    while(lo <= hi){
        if(str.charAt(lo) != str.charAt(hi)){
            return false;
        }
        lo++;
        hi--;
    }
    return true;
}

Code for palindrome with space skipping and case insensitive

boolean isPalindrome(String strs) {
		if (strs == null) 
			return false;
		char[] str = strs.toCharArray();
		int i = 0;
		int j = str.length-1;
		while (i < j && str[i] == ' ') i++;
		while (j > i && str[j] == ' ') j--;
		while (i < j) {
			if (Character.toLowerCase(str[i++]) != 
							Character.toLowerCase(str[j--]))
				return false;
			while (i < j && str[i] == ' ') i++;
			while (j > i && str[j] == ' ') j--;
		}
		return true;
	}

public class Test {
public static void main(String[] args) {
String str = "madam";
String s = "";
for(int i=0;i<str.length();i++)
{
s = s+str.charAt(i);
System.out.println(s);
}

if(str.equals(s))
{
System.out.println(str+" is palindrome");
}
else {
System.out.println(str+" is not palindrome");
}

}
}

public class CheckPalindromesInStringType {
public static void main(String[] args) {

Scanner sc=new Scanner(System.in);
System.out.println("Enter your String Type Data");
String name=sc.nextLine();
if(ispalindromes(name)){
System.out.println("is palindromes String");
}else{
System.out.println("is not palindromes String");
}


}


private static boolean ispalindromes(String name) {
int low=0;
int high=name.length()-1;
while (low<high) {
if(name.charAt(low) != name.charAt(high))
return false;
low++;
high--;
}
return true;
}

}

Given a string as input, return true if it is a palindrome (ignoring capitalisation and punctuation marks). Look at test cases.

public class Palindrome {

	static public boolean isPalindrome(String in) {
		
		boolean result = false;
        if (in == null) return result;
        
		System.out.println(in);
		StringBuilder rightway = new StringBuilder();
		StringBuilder reverse  = new StringBuilder();
		
		for (int i=0; i<in.length(); i++) {
			char c = in.charAt(i);
			if (Character.isLetter(c)) {
				rightway.append(Character.toLowerCase(c));
				reverse.insert(0,Character.toLowerCase(c));
			}
		}
		
		result = rightway.toString().length() > 0 && rightway.toString().equals(reverse.toString());
		
		if ( result ) System.out.println("We have a palindrome");
		else          System.out.println("Not a palindrome");
		
		return result;
	}
	
	public static void main(String[] args) {

		isPalindrome("");
		isPalindrome("This isn't a palindrome");
		isPalindrome("Madam, I'm Adam");
		isPalindrome("Poor Dan is in a droop");
		
	}
}

#include <string>
#include <algorithm>
#include <iostream>
int main()
{
std::string s;
std::cin >> s;
if( equal(s.begin(), s.begin() + s.size()/2, s.rbegin()) )
std::cout << "is a palindrome.\n";
else
std::cout << "is NOT a palindrome.\n";
}

if( equal(s.begin(), s.begin() + s.size()/2, s.rbegin()) )
std::cout << "is a palindrome.\n";
else
std::cout << "is NOT a palindrome.\n";

#include<algorith>

equal(str.begin(), str.end(), str.rend());

string input;

cout << "Please enter a string: ";
cin >> input;

if (input == string(input.rbegin(), input.rend())) {
cout << input << " is a palindrome";
}

public class PalindromeString {

    public static void main(String... args) {
        PalindromeString ps = new PalindromeString();
        ps.testPalindrome("Able was I ere I saw Elba");
        ps.testPalindrome("Ze de Lima, Rua Laura, Mil e Dez");
        ps.testPalindrome("Dennis and Edna sinned");
        ps.testPalindrome("Was it a car or a cat I saw?");
        ps.testPalindrome("Madam, I'm Adam");
        ps.testPalindrome("I");
        ps.testPalindrome("OO");
        ps.testPalindrome("OIO");
        ps.testPalindrome("Hello");
        ps.testPalindrome("She");
    }

    private void testPalindrome(String testString) {
        System.out.println(String.format("The string '%s' %s palindrome.", testString, (this.isPalindrome(testString) ? "is" : "is not")));
    }

    private boolean isPalindrome(String string) {
        String normalString = normalize(string);
        int half = (int) Math.floor(normalString.length() / 2);
        for (int i=0; i<half; i++) {
            int j = normalString.length() - 1 - i;
            if (normalString.charAt(i) != normalString.charAt(j)) {
                return false;
            }
        }
        return true;
    }

    private String normalize(String string) {
        return string.toLowerCase().replaceAll("\\p{Punct}|\\s", "");
    }

}

One line answer

var result = Enumerable.SequenceEqual(text.ToCharArray(), text.ToCharArray().Reverse());

bool isPalindrome(String s){
return s.equals(s.reverse());
}