[20200719] july challenge

Author: iamminji

README.md

@@ -235,3 +235,6 @@
 | [Same Tree](https://leetcode.com/explore/challenge/card/july-leetcoding-challenge/545/week-2-july-8th-july-14th/3389/)      | [python](challenge/2020/july/Same_Tree.py)  |  |
 | [3Sum](https://leetcode.com/explore/challenge/card/july-leetcoding-challenge/545/week-2-july-8th-july-14th/3384/)      | [python](challenge/2020/july/3Sum.py)  | [solutions](challenge/2020/july/3Sum.md)|
 | [Add Binary](https://leetcode.com/explore/challenge/card/july-leetcoding-challenge/546/week-3-july-15th-july-21st/3395/)      | [python](challenge/2020/july/Add_Binary.py)  | [solution](challenge/2020/july/Add_Binary.md) |
+| [Subsets](https://leetcode.com/explore/challenge/card/july-leetcoding-challenge/545/week-2-july-8th-july-14th/3387/)      | [python](challenge/2020/july/Subsets.py)  |  |
+| [Reverse Words in a String](https://leetcode.com/explore/challenge/card/july-leetcoding-challenge/546/week-3-july-15th-july-21st/3391/)      | [python](challenge/2020/july/Reverse_Words_in_a_String.py)  |  |
+| [Top K Frequent Elements](https://leetcode.com/explore/challenge/card/july-leetcoding-challenge/546/week-3-july-15th-july-21st/3393/)      | [python](challenge/2020/july/Top_K_Frequent_Elements.py)  |  |

challenge/2020/july/Reverse_Words_in_a_String.py

@@ -0,0 +1,4 @@
+class Solution:
+    def reverseWords(self, s: str) -> str:
+        return " ".join(reversed(s.split()))
+

challenge/2020/july/Subsets.py

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+from typing import List
+from copy import deepcopy
+
+
+class Solution:
+
+    def dfs(self, nums, i, inner, result):
+        result.append(deepcopy(inner))
+        for j in range(i, len(nums)):
+            inner.append(nums[j])
+            self.dfs(nums, j + 1, inner, result)
+            inner.pop()
+        return
+
+    def subsets(self, nums: List[int]) -> List[List[int]]:
+        result = []
+        self.dfs(nums, 0, [], result)
+        return result
+
+
+if __name__ == '__main__':
+    nums = [1, 2, 3]
+    sol = Solution()
+    print(sol.subsets(nums))

challenge/2020/july/Top_K_Frequent_Elements.py

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+from typing import List
+from collections import Counter
+
+
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        counter = Counter(nums)
+        counter = sorted(counter.items(), key=lambda x: -x[1])
+        result = []
+        cnt = 0
+        for item in counter:
+            if cnt == k:
+                break
+            result.append(item[0])
+            cnt += 1
+        return result
+
+
+if __name__ == '__main__':
+    nums = [1, 1, 1, 2, 2, 3]
+    k = 2
+    sol = Solution()
+    print(sol.topKFrequent(nums, k))