Valid Palindrome

https://app.gitbook.com/s/-M33ghpQv0ZbnP8UX-Qg/7.two-pointers/125.-valid-palindrome-e IsPalindrome LongestPalindrome as second variation which returns the longest palindrome in a given string or an array of strings if there are multiple of the same length.

2道找回文：2.1 在句子里忽略特殊符号大小写找回文；2.2在句子里找出所有同样长度且最长的回文， 按照原来的格式输出（保留特殊符号大小写）

class Solution {
    public boolean isPalindrome(String s) {
        
        s = s.toLowerCase();
        int left = 0;
        int right  = s.length()-1;
        while(left< right)
        {
            while(left < s.length() && !isValid(s.charAt(left)))
            {
                left++;
            }
            while(right > 0 && !isValid(s.charAt(right)))
            {
                right--;
            }
            
            if(left < right && s.charAt(left) != s.charAt(right) )
            {
                return false;
            }
            left++;
            right--;
        }
        return true;
        
    }
    
    public boolean isValid(char c)
    {
        return Character.isLetter(c) || Character.isDigit(c);
    }
}

Followup: similar as LC 5: Longest Palindromic Substring

return all longest palindrome in a string

public class AllPalindromeSubString {

    public static void main(String[] args)
    {
        String input = "babad";
        List<String> res = findAllSubString(input);
        System.out.println(res);
    }

    public static List<String> findAllSubString(String s)
    {
        List<String> res = new ArrayList<>();
    
        int maxCount = 0;
        for(int i = 0; i< s.length()-1; i++)
        {
            String s1 = getPalindromesubstring(s, i, i);
            String s2 = getPalindromesubstring(s, i, i+1);
            maxCount = Math.max(maxCount, Math.max(s1.length(), s2.length()));
            if(s1.length() == maxCount)
            {
                res.add(s1);
            }
            if(s2.length() == maxCount)
            {
                res.add(s2);
            }
        }

        Iterator<String> it = res.iterator();
        while(it.hasNext())
        {
            if(it.next().length() < maxCount)
            {
                it.remove();
            }
        }
        
        return res;
    }

    public static String getPalindromesubstring(String s , int left, int right)
    {
        while(left >=0 && right <s.length() && s.charAt(left) == s.charAt(right))
        {
            left--;
            right++;
        }
        return s.substring(left+1, right);
    }
    
}

1KB

AllPalindromeSubString.java

import java.util.*;

public class LongestPalindromicSubstring {

    public static void main(String[] args)
    {
            String s1 = "cb b d";
            List<String> res1 = getLongestPalindromicSubstring(s1);
            System.out.println(res1);
    }

    public static List<String> getLongestPalindromicSubstring(String s)
    {
        List<String> res = new ArrayList<>();
        int maxLen = 0;
        for(int i = 0; i< s.length()-1; i++)
        {
            String s1 = getPalindromicSubstring(s, i, i);
            String s2 = getPalindromicSubstring(s,i, i+1);
            maxLen = Math.max(maxLen, Math.max(s1.length(), s2.length()));
            if(s1.length() == maxLen)
            {
                res.add(s1);
            }
            if(s2.length() == maxLen)
            {
                res.add(s2);
            }
        }

        Iterator<String> it = res.iterator();
        while(it.hasNext())
        {
            if(it.next().length() < maxLen)
            {
                it.remove();
            }
        }
        return res;
    }

    public static String getPalindromicSubstring(String s, int left, int right)
    {
        while(left >=0 && !isValid(s.charAt(left)))
        {
            left--;
        }
        while(right < s.length() && !isValid(s.charAt(right)))
        {
            right++;
        }
        while(left >=0 && right < s.length() && Character.toLowerCase(s.charAt(left)) ==  Character.toLowerCase(s.charAt(right)))
        {
            left--;
            right++;
        }
        return s.substring(left+1, right);
    }

    public static boolean isValid(char c)
    {
        return Character.isLetter(c) || Character.isDigit(c);
    }
    
}