added my solution for problem 1

Python/20_Valid_parentheses.py

@@ -0,0 +1,21 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        stack = []
+        for i in range(len(s)):
+            if s[i] == "(" or s[i] == "[" or s[i] == "{": #check if an open bracket, push to stack
+                stack.append(s[i])
+            if s[i] == ")" or s[i] == "]" or s[i] == "}": #check if closing bracket, pop from stack and compare
+                if len(stack) == 0:
+                    return False
+                prev = stack.pop()
+                if prev == "(" and s[i] != ")":
+                    return False
+                if prev == "[" and s[i] != "]":
+                    return False
+                if prev == "{" and s[i] != "}":
+                    return False
+
+        if len(stack) == 0:
+            return True
+        else: 
+            return False

Python/26_Remove_Duplicates_from_Sorted_Array.py

@@ -0,0 +1,8 @@
+class Solution:
+    def removeDuplicates(self, nums: List[int]) -> int:
+        i = 1
+        while i<len(nums): #traverse array
+            if nums[i] == nums[i-1]: #if the current element is same as previous, then remove
+                nums.pop(i)
+            else:
+                i += 1

Python/TwoSum.py

@@ -0,0 +1,7 @@
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        for i in range(len(nums)):
+            for j in range(i+1, len(nums)):
+                if nums[i] + nums[j] == target:
+                    ans = [i, j]
+                    return ans