add week 3 solution

Author: rivkode

3sum/rivkode.py

@@ -0,0 +1,8 @@
+from typing import List
+
+# use hashtable
+
+class Solution:
+    def threeSum(self, nums: List[int]) -> List[List[int]]:
+        result = []
+        return result

climbing-stairs/rivkode.py

@@ -0,0 +1,20 @@
+# Time Complexity O(n)
+# - traversing for loop takes O(n)
+# Space Complexity O(n)
+# - appending for loop it takes O(n)
+
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        stage = [1, 2, 3]
+
+        for i in range(3, 45):
+            value = stage[i - 1] + stage[i - 2]
+            stage.append(value)
+
+        return stage[n - 1]
+
+if __name__ == "__main__":
+    solution = Solution()
+    result = solution.climbStairs(5)
+    print(result)
+

valid-anagram/rivkode.py

@@ -0,0 +1,26 @@
+from typing import List
+
+# Time Complexity O(n log n)
+# - when sorting by sorted function(TimSort) for each string it takes O(nlogn)
+# - traversing for loop takes O(n)
+# Space Complexity O(n)
+# - when sorting takes O(n)
+
+class Solution:
+    def isAnagram(self, s: str, t: str) -> bool:
+        s_sorted = sorted(s)
+        t_sorted = sorted(t)
+
+        for i in range(len(s_sorted)):
+            if s_sorted[i] != t_sorted[i]:
+                return False
+        return True
+
+if __name__ == "__main__":
+    solution = Solution()
+
+    s = "nagaram"
+    t = "anagram"
+
+    result = solution.isAnagram(s, t)
+    print(result)