Added Kth largest element algorithm

data_structures/arrays/kth_largest_element.py

@@ -0,0 +1,74 @@
+"""
+Given an array of integers and an integer k, find the kth largest element in the array
+
+https://stackoverflow.com/questions/251781/how-to-find-the-kth-largest-element-in-an-unsorted-array-of-length-n-in-on
+"""
+
+
+def partition(arr, low, high):
+ """
+ Partitions list based on the pivot element
+ Args:
+ arr: The list to be partitioned
+ low: The lower index of the list
+ high: The higher index of the list
+ Returns:
+ int: The index of pivot element after partitioning
+
+ Examples:
+ >>> partition([3,1,4,5,9,2,6,5,3,5],0,9)
+ 4
+ >>> partition([7,1,4,5,9,2,6,5,8],0,8)
+ 1
+ """
+ pivot = arr[high]
+ i = low - 1
+ for j in range(low, high):
+ if arr[j] >= pivot:
+ i += 1
+ arr[i], arr[j] = arr[j], arr[i]
+ arr[i + 1], arr[high] = arr[high], arr[i + 1]
+ return i + 1
+
+
+def kth_largest_element(arr, k):
+ """
+ Finds the kth largest element in a list.
+
+ Args:
+ nums : The list of numbers.
+ k : The position of the desired kth largest element.
+
+ Returns:
+ int: The kth largest element.
+
+ Examples:
+ >>> kth_largest_element([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5], 3)
+ 5
+ >>> kth_largest_element([2, 5, 6, 1, 9, 3, 8, 4, 7, 3, 5], 1)
+ 9
+ >>> kth_largest_element([9, 1, 3, 6, 7, 9, 8, 4, 2, 4, 9], 11)
+ 1
+ >>> kth_largest_element([1, 2, 4, 3, 5, 9, 7, 6, 5, 9, 3], 0)
+ 'Invalid value of k'
+ """
+ if not 1 <= k <= len(arr):
+ return "Invalid value of k"
+ low, high = 0, len(arr) - 1
+ while low <= high:
+ if low > len(arr) - 1 or high < 0:
+ return "Invalid value of k"
+ pivot_index = partition(arr, low, high)
+ if pivot_index == k - 1:
+ return arr[pivot_index]
+ elif pivot_index > k - 1:
+ high = pivot_index - 1
+ else:
+ low = pivot_index + 1
+ return "Kth largest element not found"
+
+
+if __name__ == "__main__":
+ import doctest
+
+ doctest.testmod()