找出数组中出现奇数次的整数

简单的方法，但效率不高

def find_it(seq):
    for i in seq:
        if seq.count(i)%2!=0:
            return i

效率更高

def find_it(seq):
    a = {}
    for i in seq:
        if i not in a.keys():
            a[i] = 1
        else:
            a[i] += 1
    for k,v in a.items():
        if v%2 != 0:
            return k