Find the kth largest number in an Array

K_th_largest.py

class Solution:
    # @param k & A a integer and an array
    # @return ans a integer
    def kthLargestElement(self, k, A):
        return self.helper(A, 0, len(A) - 1, k)
        
    def helper(self, arr, begin, end, k):
        pos = self.partition(arr, begin, end)
        if pos == len(arr) - k:
            return arr[pos]
        elif pos > len(arr) - k:
            return self.helper(arr, begin, pos - 1, k)
        else:
            return self.helper(arr, pos + 1, end, k)
        
        
    def partition(self, arr, begin, end):
        pos = begin
        for i in range(begin, end):
            if arr[i] < arr[end]:
                arr[i], arr[pos] = arr[pos], arr[i]
                pos += 1
        arr[pos], arr[end] = arr[end], arr[pos]
        return pos