[jylee2033] WEEK 05 solutions

best-time-to-buy-and-sell-stock/jylee2033.py

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+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        # When length is 1, no profit possible
+        if len(prices) == 1:
+            return 0
+
+        buy = 10 ** 5
+        profit = 0
+
+        # Iterate through prices
+        for price in prices:
+            # if price < buy:
+            #     buy = price
+
+            #     for j in range(i + 1, len(prices)):
+            #         if prices[j] <= buy:
+            #             continue
+
+            #         if prices[j] - buy > profit:
+            #             profit = prices[j] - buy
+            buy = min(buy, price)
+            profit = max(profit, price - buy)
+
+        return profit
+
+# Time Complexity: O(n)
+# Space Complexity: O(1)

encode-and-decode-strings/jylee2033.py

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+class Solution:
+    """
+    @param: strs: a list of strings
+    @return: encodes a list of strings to a single string.
+    """
+    def encode(self, strs):
+        # write your code here
+        # Encode each word with its length prefix and a "#"
+        # ["C#", "&"] -> "2#C#1#&"
+        encoded_str = ""
+
+        for word in strs:
+            encoded_str += f"{len(word)}#{word}"
+
+        return encoded_str
+
+    """
+    @param: str: A string
+    @return: decodes a single string to a list of strings
+    """
+    def decode(self, str):
+        # write your code here
+        # "2#C#1#&" -> ["C#", "&"]
+        decoded_lst = []
+        char_count = 0
+        reading_word = False
+        word = ""
+        length_str = ""
+
+        if str == "":
+            return [""]
+
+        for ch in str:
+            if ch == "#" and not reading_word:
+                # Finished reading the length prefix
+                # Switch to word-reading mode
+                char_count = int(length_str)
+                length_str = ""
+                reading_word = True
+
+            elif not reading_word:
+                # Accumulate digits for the length prefix
+                length_str += ch
+
+            else:
+                # reading_word is True
+                word += ch
+                char_count -= 1
+
+                if char_count == 0:
+                    reading_word = False
+                    decoded_lst.append(word)
+                    word = ""
+
+        return decoded_lst
+
+# Time Complexity: O(N)
+# Space Complexity: O(N)

group-anagrams/jylee2033.py

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+class Solution:
+    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
+        anagram_map = {}
+        for word in strs:
+            key = "".join(sorted(word))
+            if key not in anagram_map:
+                anagram_map[key] = [word]
+            else:
+                anagram_map[key].append(word)
+
+        return list(anagram_map.values())
+
+# Time Complexity: O(N * K log K), N - number of strings, K - maximum length of a string (for sorting)
+# Space Complexity: O(N * K)