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5. Longest Palindromic Substring
Medium
Given a string s, return the longest palindromic substring in s.
Example 1:
Input: s = “babad”
Output: “bab” Note: “aba” is also a valid answer.
Example 2:
Input: s = “cbbd”
Output: “bb”
Example 3:
Input: s = “a”
Output: “a”
Example 4:
Input: s = “ac”
Output: “a”
Constraints:
1 <= s.length <= 1000sconsist of only digits and English letters.
Solution
public class Solution {
public string LongestPalindrome(string s) {
if (s.Length == 1) return s;
int res = 0;
int l = 0;
int r = 0;
int len = s.Length;
for (int i = 0; i < len; i ++) {
for (int diff = 1; i - diff + 1 >= 0 && i + diff < len; diff ++) {
if (s[i - diff + 1] != s[i + diff]) break;
else if (res < diff * 2) {
res = diff * 2;
l = i - diff + 1;
r = i + diff;
}
}
}
for (int i = 0; i < len; i ++) {
for (int diff = 1; i - diff >= 0 && i + diff < len; diff ++) {
if (s[i - diff] != s[i + diff]) break;
else if (res < diff * 2 + 1) {
res = diff * 2 + 1;
l = i - diff;
r = i + diff;
}
}
}
return s.Substring(l, r - l + 1);
}
}