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 <= 1000
s consist of only digits and English letters (lower-case and/or upper-case),
Solution:
class Solution {
public:
string longestPalindrome(string s) {
int n = s.length();
int longestBegin = 0;
int maxLen = 1;
vector<vector<bool>> table(n, vector<bool>(n, false));
for (int i = 0; i < n; i++)
table[i][i] = true;
for (int i = 0; i < n-1; i++) {
if (s[i] == s[i+1]) {
table[i][i+1] = true;
longestBegin = i;
maxLen = 2;
}
}
for (int len = 3; len <= n; len++) {
for (int i = 0; i < n - len + 1; i++) {
int j = i + len - 1;
if (s[i] == s[j] && table[i+1][j-1]) {
table[i][j] = true;
longestBegin = i;
maxLen = len;
}
}
}
return s.substr(longestBegin, maxLen);
}
};