[daiyongg-kim] WEEK 05 solutions

best-time-to-buy-and-sell-stock/daiyongg-kim.py

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+class Solution:
+    def maxProfit(self, prices: List[int]) -> int:
+        min_price = prices[0]
+        max_profit = 0
+
+        for price in prices[1:]:
+            if price < min_price:
+                min_price = price
+            elif price - min_price > max_profit:
+                max_profit = price - min_price
+
+        return max_profit

encode-and-decode-strings/daiyongg-kim.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
+        result = ""
+        for word in strs:
+            word_size = len(word)
+            result += str(word_size) + "#" + word
+
+        return result
+    # input ["lint","code","love","you"]
+    # output "4#lint4#code4#love3#you"
+
+    """
+    @param: str: A string
+    @return: decodes a single string to a list of strings
+    """
+    def decode(self, str):
+        # write your code here
+        result = []
+        i = 0
+        while i < len(str):
+            j = i
+            while str[j] != "#": #find the position of '#'
+                j += 1
+
+            my_number = int(str[i:j])
+
+            start = j + 1 # add 1 to skip '#'
+            end = j + 1 + my_number
+
+            result.append(str[start:end])
+            i = end
+
+        return result
+    # input "4#lint4#code4#love3#you"
+    # output ["lint","code","love","you"]

group-anagrams/daiyongg-kim.py

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+class Solution:
+    def groupAnagrams(self, strs: List[str]) -> List[List[str]]:
+        group_anagram = defaultdict(list) 
+        # 초기화: 키가 없으면 자동으로 list() 즉, []를 실행해서 값을 만듦
+
+        for word in strs:
+            sorted_word = ''.join(sorted(word))
+            group_anagram[sorted_word].append(word)
+
+        return list(group_anagram.values())

implement-trie-prefix-tree/daiyongg-kim.py

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+class Trie:
+
+    def __init__(self):
+        self.children = {}
+        self.is_end = False
+
+    def insert(self, word: str) -> None:
+        node = self
+
+        for c in word:
+            if c not in node.children:
+                node.children[c] = Trie()
+            node = node.children[c]
+
+        node.is_end = True
+
+
+    def search(self, word: str) -> bool:
+        node = self
+
+        for c in word:
+            if c not in node.children:
+                return False
+            node = node.children[c]
+
+        return node.is_end
+
+    def startsWith(self, prefix: str) -> bool:
+        node = self
+        for c in prefix:
+            if c not in node.children:
+                return False
+            node = node.children[c]
+        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/daiyongg-kim.py

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+
+""" Failed Attempt
+ class Solution:
+     def wordBreak(self, s: str, wordDict: List[str]) -> bool:
+
+         for word in wordDict:
+             if word in s:
+                 s = s.replace(word, '')
+             else:
+                 return False
+         return len(s) == 0
+"""
+class Solution:
+    def wordBreak(self, s: str, wordDict: List[str]) -> bool:
+        word_set = set(wordDict)
+
+        dp = [False] * (len(s) + 1)
+        dp[0] = True
+
+        for i in range(1, len(s) + 1):
+            for j in range(i):
+                if dp[j] and s[j:i] in word_set:
+                    dp[i] = True
+                    break
+        return dp[len(s)]