[printjin-gmailcom] Week 05 Solutions

best-time-to-buy-and-sell-stock/printjin-gmailcom.py

@@ -0,0 +1,10 @@
+class Solution:
+    def maxProfit(self, price):
+        min_price = float('inf')
+        max_profit = 0
+        for price in prices:
+            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/printjin-gmailcom.py

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+class Solution:
+    def encode(self, strs):
+        res = ''
+        for s in strs:
+            res += str(len(s)) + '#' + s
+        return res
+
+    def decode(self, s):
+        res = []
+        i = 0
+        while i < len(s):
+            j = i
+            while s[j] != '#':
+                j += 1
+            length = int(s[i:j])
+            res.append(s[j+1:j+1+length])
+            i = j + 1 + length
+        return res

group-anagrams/printjin-gmailcom.py

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+from collections import defaultdict
+
+class Solution:
+    def groupAnagrams(self, strs):
+        anagrams = defaultdict(list)
+        for word in strs:
+            count = [0] * 26
+            for c in word:
+                count[ord(c) - ord('a')] += 1
+            anagrams[tuple(count)].append(word)
+        return list(anagrams.values())

implement-trie-prefix-tree/printjin-gmailcom.py

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+class Trie:
+    def __init__(self):
+        self.trie = {}
+
+    def insert(self, word):
+        node = self.trie
+        for char in word:
+            if char not in node:
+                node[char] = {}
+            node = node[char]
+        node['#'] = {}
+
+    def search(self, word):
+        node = self.trie
+        for char in word:
+            if char not in node:
+                return False
+            node = node[char]
+        return '#' in node
+
+    def startsWith(self, prefix):
+        node = self.trie
+        for char in prefix:
+            if char not in node:
+                return False
+            node = node[char]
+        return True

word-break/printjin-gmailcom.py

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+class Solution:
+    def wordBreak(self, s, wordDict):
+        wordSet = set(wordDict)
+        memo = {}
+
+        def backtrack(start):
+            if start == len(s):
+                return True
+            if start in memo:
+                return memo[start]
+
+            for end in range(start + 1, len(s) + 1):
+                if s[start:end] in wordSet and backtrack(end):
+                    memo[start] = True
+                    return True
+
+            memo[start] = False
+            return False
+
+        return backtrack(0)