Added two string problems

Algorithms_and_Data_Structures/Strings/longest_palindromic_substring.py

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+'''
+longest palindromic substring without DP
+We will be using a two pointer approach (l and r are the two pointers). We will be moving 
+from the middle of the string to its extreme ends and check whether the characters
+on either side of the string match.
+'''
+class longestPalindrome:
+    def longestPalindromeFinder(self, s: str) -> str:
+        #declare a variable to store the temporary length each time a palindrome is found        
+        temp_len=0
+
+        #declare a maximum length variable to store the overall maximum length
+        max_len=0
+        l=0
+        r=0
+
+        for i in range(len(s)):
+            #odd palindrome
+            #start from the middle of the string
+
+            l=i
+            r=i
+
+            #As long as the character left pointer points to and right pointer points to, match
+            #increment the right pointer and decrement the left one.
+            while(l>=0 and r<=len(s)-1 and s[l]==s[r]):
+                temp_len= r-l+1
+
+                #if a new maximum length is found, store it in the max_len variable.
+                if(temp_len>max_len):
+                    max_len=temp_len
+                    start=l
+
+                l-=1
+                r+=1
+
+            #even palindrome
+            #start from the two middle-most characters
+            l=i
+            r=i+1
+
+            #the remaining procedure remains the same as that of odd palindrome.
+            while(l>=0 and r<=len(s)-1 and s[l]==s[r]):
+                temp_len= r-l+1
+                if(temp_len>max_len):
+                    max_len=temp_len
+                    start=l
+
+                l-=1
+                r+=1
+        #return a substring of the original string which contains the longest palindrome found so far.
+        return s[start:start+max_len]
+
+#example usage
+if __name__=='__main__':
+
+    #create an instance of the class longestPalindrome and print the result
+    longest=longestPalindrome()
+    result=longest.longestPalindromeFinder("abbabab")
+    print(result)
+

Algorithms_and_Data_Structures/Strings/valid_anagram.py

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+'''
+we are going to use a hashmap approach to count the number of characters in both the strings and
+finally compare both hashmaps.
+'''
+from collections import defaultdict
+
+class valid_anagram:
+    #method to determine if two strings are valid anagrams.
+    def isAnagram(self, s: str, t: str) -> bool:
+
+        #initialize two dictionaries to be used as hashmaps.
+        dictis=defaultdict()
+        dictit=defaultdict()
+
+        #count the occurences of each character in both the strings.
+        for i in s:
+            dictis[i]=dictis.get(i,0)+1
+
+        for i in t:
+            dictit[i]=dictit.get(i,0)+1
+
+        #if both the dictionaries are the same, return True 
+        return True if dictis==dictit else False
+
+#example usage
+if __name__=='__main__':
+
+    #create an instance of the valid_anagram class.
+    anagram_checker=valid_anagram()
+
+    #call the isAnagram method
+    result = anagram_checker.isAnagram("dusty","study")
+    print(result)