solution(cpp,java): 5. Longest Palindromic Substring

5. Longest Palindromic Substring
- C++
- Java

Medium/5. Longest Palindromic Substring/Solution.cpp

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+#include <string>
+
+class Solution {
+public:
+    std::string longestPalindrome(std::string s) {
+        std::string res = "";
+        int reslen = 0;
+
+        for (int i = 0; i < s.length(); i++) {
+            // odd length
+            int left = i, right = i;
+            while (left >= 0 && right < s.length() && s[left] == s[right]) {
+                if (right - left + 1 > reslen) {
+                    res = s.substr(left, right - left + 1);
+                    reslen = right - left + 1;
+                }
+                left -= 1;
+                right += 1;
+            }
+
+            // even length;
+            left = i;
+            right = i + 1;
+            while (left >= 0 && right < s.length() && s[left] == s[right]) {
+                if (right - left + 1 > reslen) {
+                    res = s.substr(left, right - left + 1);
+                    reslen = right - left + 1;
+                }
+                left -= 1;
+                right += 1;
+            }
+        }
+        return res;
+    }
+};

Medium/5. Longest Palindromic Substring/Solution.java

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+public class Solution {
+    public String longestPalindrome(String s) {
+        String res="";
+        int reslen=0;
+
+        for(int i=0;i<s.length();i++){
+            // odd length
+            int left=i,right=i;
+            while(left>=0 && right<s.length() && s.charAt(left)==s.charAt(right)){
+                if((right-left+1)>reslen){
+                    res=s.substring(left,right+1);
+                    reslen=right-left+1;
+                }
+                left-=1;
+                right+=1;
+            }
+
+            // even length;
+            left=i;
+            right=i+1;
+            while(left>=0 && right<s.length() && s.charAt(left)==s.charAt(right)){
+                if((right-left+1)>reslen){
+                    res=s.substring(left,right+1);
+                    reslen=right-left+1;
+                }
+                left-=1;
+                right+=1;
+            }
+        }
+        return res;
+    }
+}

Medium/5. Longest Palindromic Substring/Solution.md

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+# Problem Title
+
+Longest Palindromic Substring
+
+## Problem Description
+
+Given a string s, return the longest `palindromic substring` in s.
+
+Here are some key points to understand about the problem:
+
+1. You are given a string s, and the goal is to find the longest palindromic substring within this string. 
+2. A palindromic substring is a sequence of characters that reads the same forwards as it does backward.
+3. s consist of only digits and English letters.
+
+## Method to Solve
+
+`Initialization:` Start with an empty result res and a length tracker reslen set to 0.
+
+`Iterate Through String:` For each character in the string, consider it as the center of a possible palindrome.
+
+`Odd-Length Palindromes:` Expand around the center character, checking for palindromes with odd lengths.
+
+`Even-Length Palindromes:` Also, check for palindromes with even lengths by considering adjacent characters.
+
+`Update Result:` Whenever a longer palindrome is found, update res and reslen.
+
+`Return Longest Palindrome:` After checking all centers, return the longest palindromic substring found in the string.