leetcode_gym/_problems/longestPalindromicSubstring.md

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layout	title	last_solved	category	leetcode_url	status
page	Longest Palindromic Substring		string, palindrome		Solved

Problem

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.
Example 2:

Input: "cbbd"
Output: "bb"

Solution

This only works for both even and odd palindromes but TLE on "bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb...."

{% highlight python %}

class Solution: def longestPalindrome(self, s: str) -> str:

    def isPalindrome(s):
        return s==s[::-1]
    
    longestPalindrome=""
    
    for i in range(len(s)):
        
        l=i
        r=i
        
        while l>=0 and r<len(s):

            # odd case
            currPalindrome = s[l:r+1]
            if isPalindrome(currPalindrome):
                if len(currPalindrome)>len(longestPalindrome):
                    longestPalindrome = currPalindrome
            
            # even case
            currPalindrome = s[l:r+2]
            if isPalindrome(currPalindrome):
                if len(currPalindrome)>len(longestPalindrome):
                    longestPalindrome = currPalindrome
            
            l-=1
            r+=1
    
    print(isPalindrome("bab"))
    return longestPalindrome

{% endhighlight %}

---

Same as approach above (Expand around center) but without the isPalindrome() method. I think that's what is causing it to time out.

{% highlight python %}

def longestPalindrome(self, s: str) -> str:

# return the actual palindrome
def expandAroundCenter(s, l, r):

    while l>=0 and r<len(s) and s[l]==s[r]:
        l-=1
        r+=1

    return s[l+1:r]



res = ""
for i in range(len(s)):
    oddPalin = expandAroundCenter(s, i, i)
    evenPalin = expandAroundCenter(s, i, i+1)

    if len(oddPalin)>len(res):
        res = oddPalin
    if len(evenPalin)>len(res):
        res = evenPalin

return res

{% endhighlight %}