[doh6077] WEEK 05 Solutions

best-time-to-buy-and-sell-stock/doh6077.py

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+
+# 121. Best Time to Buy and Sell Stock
+# O(n) - Two Pointers 
+class Solution:
+    def maxProfit(self, prices: list[int]) -> int:
+        left = 0 
+        right = 1
+        profit = 0
+        max_profit = 0 
+
+        while right < len(prices):
+            if prices[right] > prices[left]:
+                profit = prices[right] - prices[left]
+                max_profit = max(profit, max_profit)
+            else:
+                left = right
+            right += 1
+        return max_profit

design-add-and-search-words-data-structure/doh6077.py

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+
+# 208. Implement Trie (Prefix Tree)
+class Trie:
+
+    def __init__(self):
+        self.list = []
+
+
+    def insert(self, word: str) -> None:
+        self.list.append(word)
+
+
+    def search(self, word: str) -> bool:
+        if word in self.list:
+            return True
+        else:
+            return False 
+
+
+    def startsWith(self, prefix: str) -> bool:
+        for i, value in enumerate(self.list):
+            if value.startswith(prefix):
+                return True
+        return False
+
+
+
+# Your Trie object will be instantiated and called as such:
+# obj = Trie()
+# obj.insert(word)
+# param_2 = obj.search(word)
+# param_3 = obj.startsWith(prefix)

encode-and-decode-strings/doh6077.py

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+
+
+# 271. Encode and Decode Strings
+
+# integer represents the following word's length 
+# read until we reach to delimiter 
+
+class Solution:
+    def encode(self, strs):
+        res = ""
+        for s in strs:
+            res += str(len(s)) + "#" + s
+        return res 
+
+    def decode(self, str):
+        res, i = [], 0 
+
+        while i < len(str):
+            j = i 
+            while str[j] != "#":
+                j += 1
+            length = int(str[i:j])
+            res.append(str[j + 1 : j + 1 + length])
+            i = j + 1 + length 
+
+        return res

group-anagrams/doh6077.py

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+from collections import defaultdict
+class Solution:
+    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:  
+        # hashmap 
+        # calculate frequency 
+        # 26 alphabet characters 
+        anagrams_dict = defaultdict(list)
+        for s in strs:
+            count = [0] * 26
+            for c in s:
+                count[ord(c) - ord('a')] += 1
+
+            key = tuple(count)
+            anagrams_dict[key].append(s)
+
+        return list(anagrams_dict.values())

word-break/doh6077.py

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+class Solution:
+    def wordBreak(self, s: str, wordDict: List[str]) -> bool:
+        dp = [True] + [False] * len(s)
+
+        for i in range(1, len(s) + 1):
+            for w in wordDict:
+                start = i - len(w)
+                if start >= 0 and dp[start] and s[start:i] == w:
+                    dp[i] = True
+                    break
+
+        return dp[-1]