Merge pull request #814 from JayRajM97/master

Python and C++ code for the Longest Palindrome Substring

Author: matthewsamuel95

DP/Longest Palindrome Substring/LPS.cpp

@@ -0,0 +1,41 @@
+#include <iostream>
+#include <cstring>
+
+using namespace std;
+
+const int MAX = 1010;
+
+int memo[MAX][MAX]; 
+int lps(const string& s, int i, int j)
+{
+
+    if (i > j)
+        return 0;
+
+    if (memo[i][j] > -1)
+        return memo[i][j];
+
+    if (s[i] == s[j])
+    {
+        int equalCharacters = 2 - (i == j);
+        return memo[i][j] = equalCharacters + lps(s, i + 1, j - 1);
+    }
+    return memo[i][j] = max( lps(s, i + 1, j), lps(s, i, j - 1) );
+}
+
+int longest_palindrome(const string& s)
+{
+
+    memset(memo, -1, sizeof memo);
+    return lps(s, 0, s.length() - 1);
+}
+
+int main()
+{
+
+    cout << longest_palindrome("bbabcbcab") << '\n';
+    cout << longest_palindrome("abbaab") << '\n';
+    cout << longest_palindrome("opengenus") << '\n'; 
+
+    return 0;
+}

DP/Longest Palindrome Substring/LPS.py

@@ -0,0 +1,26 @@
+def longest_palindrome(text):
+    
+    length = len(text)
+    palindromes_lengths = [1] * length
+    for fgap in range(1, length):
+        pre = palindromes_lengths[fgap]
+        for rgap in reversed(range(0, fgap)):
+            tmp = palindromes_lengths[rgap]
+            if text[fgap] == text[rgap]:
+                if rgap + 1 > fgap - 1:
+                    palindromes_lengths[rgap] = 2
+                else:
+                    palindromes_lengths[rgap] = 2 + pre
+            else:
+                palindromes_lengths[rgap] = max(palindromes_lengths[rgap + 1],
+                                                palindromes_lengths[rgap])
+            pre = tmp
+    return palindromes_lengths[0]
+
+def main():
+    print(longest_palindrome('bbabcbcab')) 
+    print(longest_palindrome('abbaab'))    
+    print(longest_palindrome('opengenus')) 
+
+if __name__ == '__main__':
+    main()