数组中出现次数超过一半的数字

题目

数组中有一个数字出现的次数超过数组长度的一半，请找出这个数字。例如[1, 2, 3, 2, 2, 2, 5, 4, 2]。由于数字2在数组中出现了5次，超过数组长度的一半，因此输出2。

Python题解

def partition(data, start, end):
    left, right = start, end
    pivot = data[left]
    while left < right:
        while left < right and data[right] >= pivot:
            right -= 1
        data[left] = data[right]
        while left < right and data[left] <= pivot:
            left += 1
        data[right] = data[left]
    data[left] = pivot
    return left


def check_more_than_half(data, res):
    cnt = 0
    for num in data:
        if num == res:
            cnt += 1
    if cnt * 2 <= len(data):
        return False
    return True


def more_than_half_num(data):
    if data is None or len(data) == 0:
        return 0
    data_len = len(data)
    middle = data_len / 2
    start, end = 0, data_len - 1
    index = partition(data, start, end)
    while index != middle:
        if index > middle:
            end = index - 1
        else:
            start = index + 1
        index = partition(data, start, end)
    res = data[middle]
    if not check_more_than_half(data, res):
        res = 0
    return res


if __name__ == '__main__':
    data = [1, 2, 3, 2, 2, 2, 5, 4, 2]
    print more_than_half_num(data)