[freemjstudio] WEEK 1 Solutions

contains-duplicate/freemjstudio.py

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+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        first = len(nums) # O(1) : 리스트 객체는 이미 자기자신의 길이를 저장하고 있음 
+        set_nums = set(nums) # O(N)
+        second = len(set_nums)
+        return (first != second)
+
+# 시간 복잡도 : O(N)

top-k-frequent-elements/freemjstudio.py

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+import heapq
+
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        answer = []
+        count = dict()
+        heap = []
+        if len(nums) <= 1: 
+            return nums
+        # O(N)    
+        for num in nums: 
+            count[num] = count.get(num, 0) + 1
+
+        # heap 의 크기는 최대 k 로 제한함. 
+        # unique 한 M개의 숫자를 선형 순회 O(M)
+        for num, freq in count.items():
+            if len(heap) < k: 
+                heapq.heappush(heap, (freq, num))         # O(logK)
+            else: 
+                if heap[0][0] < freq:
+                    heapq.heappop(heap)         # O(logK)
+                    heapq.heappush(heap, (freq, num))         # O(logK)
+
+        for _ in range(k):
+            k, v = heapq.heappop(heap)
+            answer.append(v)
+
+        return answer 
+

two-sum/freemjstudio.py

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+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        answer = []
+        hashmap = dict()
+        for i in range(len(nums)):
+            current_num = nums[i]
+            diff = target - current_num
+            if diff in hashmap.keys(): 
+                return [i, hashmap[diff]] 
+            hashmap[current_num] = i # store the index of current num
+
+        return answer