大小为n的数组,其中一个元素为n/2次

def find_element(arr):
    n = len(arr)
    element_count = {}
    for i in range(n):
        if arr[i] in element_count:
            element_count[arr[i]] += 1
        else:
            element_count[arr[i]] = 1
    for element, count in element_count.items():
        if count == n/2:
            return element
    return None