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()