addition of longest palindrome substring

Author: VeldaKiara

longest_palindrome.py

@@ -0,0 +1,40 @@
+# Given a string s, return the longest palindromic substring in s.
+# Constraints: 1 <= s.length <= 1000
+# s consist of only digits and English letters (lower-case and/or upper-case)
+
+class Solution:
+    def longestPalindrome(self, s: str) -> str:
+        vel = [[False for i in range(len(s))] for i in range(len(s))]
+        for i in range(len(s)):
+            vel[i][i] = True
+        max_len = 1
+        start = 0
+        for k in range (2, len(s)+1):
+            for i in range (len(s)-k+1):
+                end = i + k
+                if  k == 2:
+                    if s[i] == s[end-1]:
+                        vel[i][end-1]=True
+                        max_len = k
+                        start = i
+                else:
+                    if s[i] == s[end-1] and vel[i+1][end-2]:
+                        vel[i][end-1]=True
+                        max_len = k
+                        start = i
+        return s[start:start+max_len]
+
+# How I solved it 
+# Define one square matrix of order same as the length of string, and fill it with False
+# Set the major diagonal elements as true, so Vel[i, i] = True for all i from 0 to order – 1
+# start := 0
+# for k in range 2 to length of S + 1
+# for i in range 0 to length of S – k + 1
+# end := i + k
+# if k = 2, then
+# if S[i] = S[end - 1], then
+# vel[i, end - 1] = True, max_len := k, and start := i
+# otherwise
+# if S[i] = S[end - 1] and vel[i + 1, end - 2], then
+# vel[i, end - 1] = True, max_len := k, and start := i
+# return a substring of from index start to start + max_len