[WHYjun] WEEK 01 solutions - (3/5)

Author: WHYjun

contains-duplicate/WHYjun.py

@@ -0,0 +1,3 @@
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        return len(set(nums)) != len(nums)

top-k-frequent-elements/WHYjun.py

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+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        # Time complexity: O(nlogn)
+        # Space Complexity: O(n)
+        
+        if len(nums) <= k:
+            return list(set(nums))
+
+        counts = {}
+        for num in nums:
+            if num not in counts:
+                counts[num] = 0
+            counts[num] += 1
+        
+        # The key of dictionary is unique.
+        sortedKeys = sorted(list(counts.keys()), key=lambda key: counts[key], reverse = True)
+        return sortedKeys[:k]

two-sum/WHYjun.py

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+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        memo = {}
+
+        for i, num in enumerate(nums):
+            diff = target - num
+            if diff in memo:
+                # Each input would have exactly one solution
+                return [memo[diff], i]
+            memo[num] = i    
+            
+        return []