[i-mprovising] Week 01 solutions

contains-duplicate/i-mprovising.py

@@ -0,0 +1,11 @@
+"""
+O(n) complexity
+"""
+
+
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        nums_set = set(nums)
+        if len(nums) == len(nums_set):
+            return False
+        return True

house-robber/i-mprovising.py

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+"""
+Time complexity O(n)
+"""
+
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        n = len(nums)
+        if n == 1:
+            return nums[0]
+        dp = [nums[0], max([nums[0], nums[1]])]
+        if n == 2:
+            return dp[1]
+
+        for i in range(2, n):
+            num = nums[i]
+            tmp = [
+                dp[i-2] + num,
+                dp[i-1]
+            ]
+            dp.append(max(tmp))
+        return dp[-1]

longest-consecutive-sequence/i-mprovising.py

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+"""
+Time complexity O(n)
+"""
+
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        num_set = set(nums) # hash table
+        longest = 0
+
+        for n in num_set:
+            if n-1 in num_set:
+                continue
+            cur_len = 1
+            while n + cur_len in num_set:
+                cur_len += 1
+
+            longest = max(longest, cur_len)
+
+        return longest

top-k-frequent-elements/i-mprovising.py

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+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        """O(nlogn) complexity"""
+        frequency = defaultdict(int)
+        for n in nums:
+            frequency[n] += 1
+        sorted_frequency = sorted(frequency.items(), key=lambda x:x[1], reverse=True)
+        answer = []
+        for i in range(k):
+            answer.append(sorted_frequency[i][0])
+        return answer

two-sum/i-mprovising.py

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+"""
+hash table
+O(n) complexity
+"""
+
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        table = {num:idx for idx, num in enumerate(nums)}
+        for i, x in enumerate(nums):
+            y = target - x
+            if (y in table) and table[y] != i:
+                return [i, table[y]]