Added Kth largest element algorithm

data_structures/arrays/kth_largest_element.py

@@ -0,0 +1,83 @@
+"""
+Given an array of integers and an integer k, find the kth largest element in the array
+
+https://stackoverflow.com/questions/251781
+"""
+
+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
+ >>> partition(['apple', 'cherry', 'date','banana'], 0, 3)
+ 2
+ >>> partition([3.1, 1.2, 5.6, 4.7], 0, 3)
+ 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([3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5], 2.5)
+ -1
+ >>> kth_largest_element([2, 5, 6, 1, 9, 3, 8, 4, 7, 3, 5], 1)
+ 9
+ >>> kth_largest_element([2, 5, 6, 1, 9, 3, 8, 4, 7, 3, 5], -2)
+ -1
+ >>> 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)
+ -1
+ >>> kth_largest_element(['apple', 'cherry', 'date','banana'], 2)
+ 'cherry'
+ >>> kth_largest_element([3.1, 1.2, 5.6, 4.7,7.9,5,0], 2)
+ 5.6
+ >>> kth_largest_element([3.1, 1.2, 5.6, 4.7,7.9,5,0], 1.5)
+ -1
+ """
+ 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()