[doh6077] WEEK 01 solutions

contains-duplicate/doh6077.py

@@ -1,10 +1,7 @@
+# https://leetcode.com/problems/contains-duplicate/description/
 
-# set에 저장하면서 중복 여부 확인하기
 class Solution:
-    def containsDuplicate(self, nums: list[int]) -> bool:
-        hashset = set()
-        for i in nums:
-            if i in hashset:
-                return True
-            hashset.add(i)
-        return False
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        # Create a set to store unique numbers from nums
+        nums_set = set(nums)
+        return len(nums_set) != len(nums)

longest-consecutive-sequence/doh6077.py

@@ -1,4 +1,5 @@
 # 배열을 정렬하고 포인터를 두개 사용
+"""
 class Solution:
     def longestConsecutive(self, nums: List[int]) -> int:
         if not nums:
@@ -32,3 +33,32 @@ def longestConsecutive(self, nums: List[int]) -> int:
                 r += 1
 
         return longest
+"""
+from typing import List
+
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        if len(nums) <= 1:
+            return len(nums)
+
+        nums.sort()
+        r = 1
+        curr = nums[0]
+        count = 1
+        max_count = 1
+
+        while r < len(nums):
+            if nums[r] == curr:
+                r += 1
+                continue
+
+            if nums[r] == curr + 1:
+                count += 1
+            else:
+                count = 1
+
+            curr = nums[r]
+            max_count = max(max_count, count)
+            r += 1
+
+        return max_count

top-k-frequent-elements/doh6077.py

@@ -1,12 +1,36 @@
+
+# 6기 
+# class Solution:
+#     # dictionary use 
+#     def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+#         result = {}  # key: 원소, value: 등장 횟수
+#         for n in nums:
+#             if n in result:
+#                 result[n] = result[n] + 1
+#             else:
+#                 result[n] = 1
+
+#         # 가장 자주 등장한 원소 k개 반환
+#         return sorted(result.keys(), key=lambda x: result[x], reverse=True)[:k]
+
+# 7기 
 class Solution:
-    # dictionary use 
     def topKFrequent(self, nums: List[int], k: int) -> List[int]:
-        result = {}  # key: 원소, value: 등장 횟수
-        for n in nums:
-            if n in result:
-                result[n] = result[n] + 1
+        # 1. Count frequency of each number
+        freq = {}
+
+        for num in nums:
+            if num not in freq:
+                freq[num] = 1
             else:
-                result[n] = 1
+                freq[num] += 1
+
+        # 2. Sort by frequency in descending order
+        sorted_items = sorted(freq.items(), key=lambda item: item[1], reverse=True)
+
+        # 3. Take the first k elements
+        result = []
+        for i in range(k):
+            result.append(sorted_items[i][0])
 
-        # 가장 자주 등장한 원소 k개 반환
-        return sorted(result.keys(), key=lambda x: result[x], reverse=True)[:k]
+        return result

two-sum/doh6077.py

@@ -1,8 +1,24 @@
+# 6기 
+# class Solution:
+#     def twoSum(self, nums: list[int], target: int) -> list[int]:
+#         prevMap = {} # val : index 
+#         for i, n in enumerate(nums):
+#             diff = target - n 
+#             if diff in prevMap:
+#                 return [prevMap[diff], i]
+#             prevMap[n] = i 
+
+# 7기 
+# https://leetcode.com/problems/two-sum/description/
 class Solution:
-    def twoSum(self, nums: list[int], target: int) -> list[int]:
-        prevMap = {} # val : index 
-        for i, n in enumerate(nums):
-            diff = target - n 
-            if diff in prevMap:
-                return [prevMap[diff], i]
-            prevMap[n] = i 
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        # use Hash map to save num and index 
+        nums_hm = {}
+
+        for i, num in enumerate(nums):
+            find_val = target - num
+
+            if find_val in nums_hm:
+                return [nums_hm[find_val], i]
+
+            nums_hm[num] = i