[devyulbae] WEEK 01 solutions

[devyulbae] WEEK 01 solutions

Author: devyulbae

contains-duplicate/devyulbae.py

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+"""
+Blind75 - 1. Contains Duplicate
+https://leetcode.com/problems/contains-duplicate/
+
+Counter를 사용한 풀이
+Counter 생성에 n번, 조회에 n번 -> O(n)
+"""
+from typing import List
+from collections import Counter
+
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        counter = Counter(nums)
+        for count in counter.values():
+            if count > 1:
+                return True
+            
+        return False
+    

house-robber/devyulbae.py

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+"""
+blind75 - House Robber
+LeetCode Problem: https://leetcode.com/problems/house-robber/
+
+재귀
+F(x) = F(x+1), F(x+2) + nums[x] 중 큰 값을 계속 선택하면 된다
+-> 재귀를 2번씩 호출하기 때문에 시간복잡도는 O(2^n)으로 Time Limit Exceeded 발생
+다음 주차 때 다시 풀어보자.
+dp로도 될 거 같다
+"""
+
+from typing import List
+
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        if not nums:
+            return 0
+        
+        memo = {}
+
+        def dfs(s, memo):
+            if s >= len(nums):
+                return 0
+            if s+1 in memo:
+                prev1 = memo[s+1]
+            else:
+                prev1 = dfs(s+1, memo)
+                memo[s+1] = prev1
+            
+            if s+2 in memo:
+                prev2 = memo[s+2]
+            else:
+                prev2 = dfs(s+2, memo)
+                memo[s+2] = prev2
+
+            return max(prev1, prev2 + nums[s])
+        
+        return dfs(0, memo)
+        

longest-consecutive-sequence/devyulbae.py

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+"""
+Blind75 - Longest Consecutive Sequence
+https://leetcode.com/problems/longest-consecutive-sequence/
+
+조건 : O(n) 시간복잡도
+1. 시작점이면 초기화
+2. 아니면 cnt++
+3. 끊기면 max 갱신
+"""
+from typing import List
+
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        if len(nums) == 0:
+            return 0
+        nums.sort()
+        length = 1
+        max_length = 0
+        for i in range(len(nums)-1):
+            if nums[i+1] == nums[i]:
+                continue
+            elif nums[i+1] == nums[i] + 1:
+                length += 1
+            else:
+                max_length = max(max_length, length)
+                length = 1
+        
+        max_length = max(max_length, length)
+        return max_length
+

top-k-frequent-elements/devyulbae.py

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+"""
+Blind75 - top-k-frequent-elements
+https://leetcode.com/problems/top-k-frequent-elements/
+"""
+
+from typing import List
+from collections import Counter
+
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        # (1,1,2,2,2,3) -> {1:1, 2:3, 3:1}
+        num_counter = Counter(nums) 
+        # {1:1, 2:3, 3:1} -> [(2,3), (1,1), (3,1)]
+        sorted_items = sorted(num_counter.items(), key=lambda x: x[1], reverse=True)
+        return [item[0] for item in sorted_items[:k]]
+    

two-sum/devyulbae.py

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+"""
+https://leetcode.com/problems/two-sum/
+"""
+from typing import List
+
+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]
+