[thispath98] Week 6

best-time-to-buy-and-sell-stock/thispath98.py

@@ -0,0 +1,12 @@
+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        minimum = prices[0]
+        answer = 0
+        for i in range(1, len(prices)):
+            if minimum > prices[i]:
+                minimum = prices[i]
+            else:
+                diff = prices[i] - minimum
+                if answer < diff:
+                    answer = diff
+        return answer

encode-and-decode-strings/thispath98.py

@@ -0,0 +1,6 @@
+class Codec:
+    def encode(self, strs: List[str]) -> str:
+        return "\n".join(strs)
+
+    def decode(self, s: str) -> List[str]:
+        return s.split("\n")

group-anagrams/thispath98.py

@@ -0,0 +1,10 @@
+from collections import defaultdict
+
+class Solution:
+    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
+        anagram_dict = defaultdict(list)
+        for string in strs:
+            anagram_dict[tuple(sorted(string))].append(string)
+
+        answer = list(anagram_dict.values())
+        return answer

implement-trie-prefix-tree/thispath98.py

@@ -0,0 +1,42 @@
+class Node:
+    def __init__(self, is_end=False):
+        self.child = {}
+        self.is_end = is_end
+
+
+class Trie:
+    def __init__(self):
+        self.root = Node()
+
+    def insert(self, word: str) -> None:
+        node = self.root
+        for ch in word:
+            if ch not in node.child:
+                node.child[ch] = Node()
+            node = node.child[ch]
+        node.is_end = True
+
+    def search(self, word: str) -> bool:
+        node = self.root
+        for ch in word:
+            if ch not in node.child:
+                return False
+            node = node.child[ch]
+
+        return node.is_end
+
+    def startsWith(self, prefix: str) -> bool:
+        node = self.root
+        for ch in prefix:
+            if ch not in node.child:
+                return False
+            node = node.child[ch]
+
+        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)

valid-parentheses/thispath98.py

@@ -0,0 +1,34 @@
+class Solution:
+    def isValid(self, s: str) -> bool:
+        """
+        Intuition:
+            stack 자료구조를 사용해서 닫히는 괄호가 올 경우
+            stack의 마지막과 일치하는지 확인한다.
+
+        Time Complexity:
+            O(N):
+                문자열을 한번 스캔하면서 조건문을 확인하므로
+                O(N)의 시간복잡도가 소요된다.
+
+        Space Complexity:
+            O(N):
+                최악의 경우 문자열 개수만큼 stack에 저장한다.
+        """
+        stack = []
+        for ch in s:
+            if ch in ["(", "{", "["]:
+                stack.append(ch)
+            elif ch in [")", "}", "]"]:
+                if stack and (
+                    (ch == ")" and stack[-1] == "(")
+                    or (ch == "}" and stack[-1] == "{")
+                    or (ch == "]" and stack[-1] == "[")
+                ):
+                    stack.pop()
+                else:
+                    return False
+
+        if stack:
+            return False
+        else:
+            return True

word-break/thispath98.py

@@ -0,0 +1,20 @@
+class Solution:
+    def wordBreak(self, s: str, wordDict: List[str]) -> bool:
+        checked = set()
+
+        def dfs(idx):
+            if idx in checked:
+                return
+            checked.add(idx)
+
+            if idx == len(s):
+                return True
+
+            for word in wordDict:
+                word_len = len(word)
+                if s[idx: idx + word_len] == word:
+                    if dfs(idx + word_len):
+                        return True
+            return False
+
+        return dfs(0)