[changhyumm] WEEK 01 solutions

contains-duplicate/changhyumm.py

@@ -0,0 +1,9 @@
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        dic = dict()
+        for num in nums:
+            if num in dic:
+                return True
+            else:
+                dic[num] = True
+        return False

house-robber/changhyumm.py

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+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        n = len(nums)
+        # 집이 하나면 최대 profit은 그 자체
+        if n == 1:
+            return nums[0]
+
+        # dp[i]를 i+1 집까지 털었을때의 max라고 정의
+        # dp[i] = max(dp[i-1], nums[i] + dp[i-2])
+        dp = [0] * n
+        dp[0] = nums[0]
+        dp[1] = max(nums[0], nums[1])
+
+        # dp를 누적
+        for i in range(2, n):
+            dp[i] = max(dp[i-1], nums[i] + dp[i-2])
+
+        # time O(n) - loop 1번
+        # space O(n) - dp 배열 
+        return dp[-1]

longest-consecutive-sequence/changhyumm.py

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+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        num_set = set(nums)
+        max_length = 0
+
+        for num in num_set:
+            if num - 1 not in num_set:
+                length = 1
+                while num + length in num_set:
+                    length += 1
+                max_length = max(max_length, length)
+        return max_length

top-k-frequent-elements/changhyumm.py

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+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        freq = dict()
+        for num in nums:
+            if num in freq:
+                freq[num] += 1
+            else:
+                freq[num] = 1
+
+        result = sorted(freq.items(), key=lambda x: x[1], reverse=True)
+        ans = []
+        idx = 0
+        while k > 0:
+            ans.append(result[idx][0])
+            idx += 1
+            k -= 1
+        return ans

two-sum/changhyumm.py

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+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]
+        dic = dict()
+        for idx, num in enumerate(nums):
+            if target - num in dic:
+                return [idx, dic[target-num]] 
+            else:
+                dic[num] = idx