This question is part of NeetCode150 series.
Problem Description
Given a string s, return the longest palindromic substring in s.
Solution
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class Solution {
//Time complexity: O(n^2)
public String longestPalindrome(String s) {
String ans = "";
//At every index, check for longest palindrome substring
for(int i=0; i<s.length(); i++){
//odd length
String oddString = palindromeHelper(s, i, i);
if(oddString.length() > ans.length()){
ans = oddString;
}
//even length
String evenString = palindromeHelper(s, i, i+1);
if(evenString.length() > ans.length()){
ans = evenString;
}
}
return ans;
}
public String palindromeHelper(String s, int l, int r){
int start = -1;
int end = -1;
while(l>=0 && r<s.length() && s.charAt(l) == s.charAt(r)){
start = l;
end = r;
l--;
r++;
}
if(start == -1) return "";
return s.substring(l+1, r);
}
}
Further Reading: Manacher’s algorithm | O(n) solution