[Leo] 5th Week solutions

Author: leokim0922

encode-and-decode-strings/Leo.py

@@ -0,0 +1,26 @@
+class Codec:
+    def encode(self, strs: List[str]) -> str:
+        """Encodes a list of strings to a single string.
+        """
+        res = ''
+
+        for s in strs:
+            res += str(len(s)) + '#' + s
+
+        return res
+
+    def decode(self, s: str) -> List[str]:
+        """Decodes a single string to a list of strings.
+        """
+        res = []
+
+        i = 0
+        while i < len(s):
+            a = s.find('#', i)
+            length = int(s[i:a])
+            res.append(s[a + 1:a + 1 + length])
+            i = a + 1 + length
+
+        return res
+
+        ## TC: O(n), SC:O(n),n denotes sum of all len(s)

top-k-frequent-elements/Leo.py

@@ -0,0 +1,17 @@
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+
+        num_dict = collections.Counter(nums)
+        freq = num_dict.most_common()
+        ans = []
+
+        for key, val in freq:
+            if k == 0:
+                break
+
+            ans.append(key)
+            k -= 1
+
+        return ans
+
+        ## TC: O(n * logn), SC: O(n)