出現次數超過了一半，那就用一個count計數，相等加1，不等減1，count<0就更換res

class Solution(object):
    def majorityElement(self, nums):
        """
        :type nums: List[int]
        :rtype: int
        """
        
        res=nums[0]
        count = 0
        for num in nums:
            if res == num:
                count +=
 
1 
            else:
                count -=1 
            if count < 0:
                res = num 
                count = 1
        return res