Create 215-kth_largest_elem_in_array.py

Author: stevestar888

Diff for: 215-kth_largest_elem_in_array.py

@@ -0,0 +1,85 @@
+import heapq
+
+"""
+https://leetcode.com/problems/kth-largest-element-in-an-array/
+
+Strat: Use a heap. Building it with the built-in library (documentation:
+    https://docs.python.org/2/library/heapq.html#heapq.heapify). After it's
+    built, just remove (nums - k) numbers from it. The last number you 
+    remove will be the k-th largest number.
+
+Can also use QuickSelect, with average runtime of O(n), but it's not guranteed
+    https://en.wikipedia.org/wiki/Quickselect
+"""
+
+class Solution(object):
+    def findKthLargest(self, nums, k):
+        """
+        :type nums: List[int]
+        :type k: int
+        :rtype: int
+        """
+        heapq.heapify(nums) #turn nums from a list into a min heap
+        
+        for _ in range(len(nums) + 1 - k):
+            elem = heapq.heappop(nums)
+        
+        return elem
+        
+    def findKthLargest(self, nums, k):
+        """
+        :type nums: List[int]
+        :type k: int
+        :rtype: int
+        """
+        heapq.heapify(nums) 
+        
+        k_largest = heapq.nlargest(k, nums) #grab the list of k largest nums
+        return k_largest[-1] #last elem of nlargest
+    
+    
+"""
+A nice quick select I found
+"""
+# from random import randint
+
+# class Solution(object):
+#     def findKthLargest(self, nums, k):
+#         """
+#         :type nums: List[int]
+#         :type k: int
+#         :rtype: int
+#         """
+#         def partition(p, r):
+#             x = nums[r]
+#             i = p-1
+#             for j in range(p,r):
+#                 if nums[j] < x:
+#                     i += 1
+#                     nums[i], nums[j] = nums[j], nums[i]
+#             nums[i+1],nums[r] = nums[r], nums[i+1]    
+#             return i+1
+        
+#         def random_partition(p,r):
+#             ri = randint(p,r)
+#             nums[ri], nums[r] = nums[r], nums[ri]
+#             return partition(p, r) 
+            
+#         def select(p, r, k):
+#             if p == r:
+#                 return nums[p]
+#             q = random_partition(p, r)
+#             i = q-p+1
+#             if i == k:
+#                 return nums[q]
+#             elif k < i:
+#                 return select(p, q-1, k)
+#             else:
+#                 return select(q+1, r, k-i)
+
+#         return select(0, len(nums)-1, len(nums)-k+1)   
+
+
+
+sol = Solution().findKthLargest([1,4,6,3,2], 2)
+print(sol)