Longest Palindromic Substring | Leetcode solution

Given a string s, return the longest 

palindromic substring in s.

 

Example 1:

Input: s = "babad"
Output: "bab"
Explanation: "aba" is also a valid answer.

Example 2:

Input: s = "cbbd"
Output: "bb"

 

Constraints:

• 1 <= s.length <= 1000
• s consist of only digits and English letters.

 Code(C++):-

class Solution {

public:

string longestPalindrome(string s) {

int n=s.size();

int dp[n][n];

memset(dp,0,n*n*sizeof(int));

for(int i=0;i<n;i++)

dp[i][i]=1;

int maxlength=1;

int starting =0;

for(int i=0;i<n-1;i++)

{

if(s[i]==s[i+1])

{

starting=i;

dp[i][i+1]=1;

maxlength=2;

}

}

// for substring greater than 2

for(int k=3;k<=n;k++)

{

for(int i=0;i<=n-k;i++)

{

int j=i+k-1;

if(dp[i+1][j-1] and s[i]==s[j])

{

if(k>maxlength)

{

maxlength=k;

starting=i;

}

dp[i][j]=1;

}

}

}

string ans="";

for(int i=starting;i<starting+maxlength;i++)

{

ans+=(s[i]);

}

return ans;

}

};

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