[Chanz] WEEK 05 Solutions

best-time-to-buy-and-sell-stock/Chanz82.py

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+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+
+        # set buy, sell as index of the prices
+        buy = 0
+        sell = 1
+
+        max_profit = 0
+
+        while sell < len(prices): # loop until we checked last prices
+            if prices[buy] > prices[sell]:
+                buy = sell # found low price for buying
+            else :
+                profit = prices[sell] - prices[buy]
+                max_profit = max(profit, max_profit)
+
+            sell += 1 # next sell price
+
+        return max_profit
+

encode-and-decode-strings/Chanz82.py

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+class Solution:
+
+    def encode(self, strs: List[str]) -> str:
+        encoded_string = ""
+
+        for plain_string in strs:
+            encoded_string = encoded_string + str(len(plain_string)) + ";" + plain_string
+
+        #print(encoded_string)
+        return encoded_string
+
+    def decode(self, s: str) -> List[str]:
+        decoded_str_list = []
+        idx = 0
+        while idx < len(s):
+            idx_del = s.index(";", idx)
+            #print(s[idx:idx_del])
+            size = int(s[idx:idx_del])
+            start_idx = idx_del+1
+            decoded_str_list.append(s[start_idx:start_idx+size])
+            idx = start_idx + size
+        return decoded_str_list

group-anagrams/Chanz82.py

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+
+from collections import defaultdict
+class Solution:
+    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
+
+        result = defaultdict(list)
+        for word in strs:
+            key = ''.join(sorted(word)) 
+            result[key].append(word)
+
+        return list(result.values())

implement-trie-prefix-tree/Chanz82.py

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+class Trie:
+
+    def __init__(self):
+        self.root_map = dict()
+
+    def insert(self, word: str) -> None:
+        idx = 0
+        search_map = self.root_map
+        while idx < len(word):
+            key = ord(word[idx])
+            if key not in search_map:
+                search_map[key] = dict()
+            search_map = search_map[key]
+            idx += 1
+        search_map['#'] = True
+
+    def search(self, word: str) -> bool:
+        idx = 0
+        search_map = self.root_map
+        while idx < len(word):
+            key = ord(word[idx])
+            if key not in search_map:
+                return False
+            search_map = search_map[key]
+            idx += 1
+        return '#' in search_map
+
+
+    def startsWith(self, prefix: str) -> bool:
+        idx = 0
+        search_map = self.root_map
+        while idx < len(prefix):
+            key = ord(prefix[idx])
+            if key not in search_map:
+                return False
+            search_map = search_map[key]
+            idx += 1
+        return True
+
+
+# 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)

word-break/Chanz82.py

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+class Solution:
+    def wordBreak(self, s: str, wordDict: List[str]) -> bool:
+
+        visited = set()
+
+        def dfs(start):
+            if start == len(s):
+                return True
+
+            if start in visited:
+                return False
+
+            for word in wordDict:
+                if s[start:start+len(word)] == word:
+                    if dfs(start+len(word)):
+                        return True
+
+            visited.add(start)
+            return False
+
+        return dfs(0)
+