diff --git a/001_Two_Sum.py b/001_Two_Sum.py
index 1a16a00..92a5b46 100644
--- a/001_Two_Sum.py
+++ b/001_Two_Sum.py
@@ -1,17 +1,6 @@
 class Solution:
     def twoSum(self, nums: List[int], target: int) -> List[int]:
-        # nums_index = list(enumerate(nums))
-        # nums_index.sort()
-        # print(nums)
         for i in range(len(nums)):
             complement = target-nums[i]
             if complement in nums and nums.index(complement) != i:
                 return [i,nums.index(complement)]
-        # for i in range(len(nums)-1):
-        #     j=i+1
-        #     while j < len(nums):
-        #         if nums[i]+nums[j]==target:
-        #             return [i, j]
-        #         j += 1
-        #     i += 1
-        # return result
diff --git a/013_Roman_To_Integer.py b/013_Roman_To_Integer.py
index f65b778..96dfd4b 100644
--- a/013_Roman_To_Integer.py
+++ b/013_Roman_To_Integer.py
@@ -1,17 +1,43 @@
-#convert Roman to Integer
 class Solution:
-    # @param {string} s
-    # @return {integer}
-    def romanToInt(self, s):
-        roman = {'M': 1000,'D': 500 ,'C': 100,'L': 50,'X': 10,'V': 5,'I': 1}
-        
-        result = 0
-        for i in range(len(s)-1):
-            if roman[s[i]]<roman[s[i+1]]:
-                result-=roman[s[i]]
+    def romanToInt(self, s: str) -> int:
+        roman = {
+            'I':1,
+            'V':5,
+            'X':10,
+            'L':50,
+            'C':100,
+            'D':500,
+            'M':1000
+        }
+        s=s.replace('IV', 'IIII').replace('IX','IIIIIIIII')
+        s=s.replace('XL', 'XXXX').replace('XC','XXXXXXXXX')
+        s=s.replace('CD', 'CCCC').replace('CM','CCCCCCCCC')
+
+        L = []
+        temp = s[0]
+        for i in range(1,len(s)):
+            if s[i] == s[i-1]:
+                temp += s[i]
             else:
-                result+=roman[s[i]]
-        else:
-            result+=roman[s[-1]]
-        
-        return result
+                L.append(temp)
+                temp = s[i]
+            if i == len(s)-1:
+                L.append(temp)
+        sum = 0
+        for i in L:
+            print(i)
+            if i[0] == 'M':
+                sum += roman['M'] * len(i)
+            elif i[0] =='C':
+                sum += roman['C'] * len(i)
+            elif i[0] =='D':
+                sum += roman['D'] * len(i)
+            elif i[0] =='L':
+                sum += roman['L'] * len(i)
+            elif i[0] =='X':
+                sum += roman['X'] * len(i)
+            elif i[0] =='V':
+                sum += roman['V'] * len(i)
+            elif i[0] =='I':
+                sum += roman['I'] * len(i)
+        return sum
diff --git a/020_Valid_Parentheses.py b/020_Valid_Parentheses.py
new file mode 100644
index 0000000..3e3698f
--- /dev/null
+++ b/020_Valid_Parentheses.py
@@ -0,0 +1,8 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        while s:
+            if '{}' in s: s = s.replace('{}', '')
+            elif '[]' in s: s = s.replace('[]', '')
+            elif '()' in s: s = s.replace('()', '')
+            else: return False
+        return True