[sangbeenmoon] WEEK 1 Solutions

contains-duplicate/sangbeenmoon.py

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+# time : O(n)
+# space : O(n)
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        d = {}
+        for num in nums:
+            if num in d:
+                return True
+            else:
+                d[num] = True
+        return False

house-robber/sangbeenmoon.py

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+# dp[i] = max(dp[i-2] + nums[i] , dp[i-1])
+# time : O(n)
+# space : O(n)
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        dp = [0] * len(nums)
+        dp[0] = nums[0]
+
+        if len(nums) == 1:
+            return dp[0]
+
+        dp[1] = max(dp[0], nums[1])
+        for i in range(2, len(nums)):
+            dp[i] = max(dp[i-2] + nums[i] , dp[i-1])
+
+        return dp[len(nums) - 1]

longest-consecutive-sequence/sangbeenmoon.py

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+# 30분 내로 풀지 못함. 풀이를 참고하였음.
+# idea : x - 1 이 존재하지 않는 x 값에서만 loop 를 실행한다.
+# time O(n) : 모든 숫자를 많아야 1,2번 방문.
+# space O(n)
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        s = set(nums)
+        answer = 0
+        for num in s:
+            if num - 1 not in s:
+                cur = num - 1
+                length = 0
+                while cur + 1 in s:
+                    cur = cur + 1
+                    length = length + 1
+                answer = max(answer , length)
+
+        return answer

top-k-frequent-elements/sangbeenmoon.py

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+# idea
+# 1. 빈도수를 dict 에 저장한다.
+# 2. 빈도수 내림차순으로 정렬한다.
+# 3. 2에서 정렬한 entry 중 1번째, 2번째, ... k 번째 key 값을 모아서 List 로 반환한다.
+# time : O(nlogn)
+# space : O(n)
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        count_dict = {}
+
+        for num in nums:
+            if num in count_dict:
+                count_dict[num] = count_dict[num] + 1
+            else:
+                count_dict[num] = 1
+
+        tuple_list = []
+
+        for (count_key, count_value) in count_dict.items():
+            tuple_list.append((count_key, count_value))
+
+        sorted_tuple_list = sorted(tuple_list, key=lambda x: x[1], reverse=True)
+        answer = []
+
+        for i in range(k):
+            answer.append(sorted_tuple_list[i][0])
+
+        return answer
+
+
+

two-sum/sangbeenmoon.py

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+# time : O(n^2)
+# space : O(1)
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:        
+        for i in range(len(nums)):
+            for j in range(i + 1, len(nums)):
+                if nums[i] + nums[j] == target:
+                    return [i,j]
+