样例题：https://codeforces.com/contest/1234/problem/B1

主要是需要对每个数字 Ai 保存的位置进行记录，Ai 最大是1e9，会导致数组保存不了，于是想到python中的list

list声明：

mylist = []
print (type(mylist))

list增加：

list = [1,2,3,4]
list.append(5)
list.insert(2,6)
print (list)
#[1,2,6,3,4,5]

list删除：

####
x = list.pop()
#x = 5
#list = [1,2,6,3,4]

list.remove(7)
#ValueError: list.remove(x): x not in list

list.remove(6)
print (list)
#list = [1,2,3,4]

list修改：

####
list[1] = 10
print (list)
#list = [1, 10, 3, 4]

list查找：

#list = [1, 10, 3, 4]
list.count(1)
#1
list.count(0)
#0
list.index(1)
#0
list.index(3)
#2
list.index(0)
#ValueError: 0 is not in list

if 0 in list:
    print ("0 is in list")
else:
    print ("0 is not in list")

其他操作：

list = [1, 10, 3, 4, 'a', 'Aa', 'Abb', 'Aba']
list.reverse()
list = list[::-1]

list.sort()
#list = [1, 3, 4, 10, 'Aa', 'Aba', 'Abb', 'a']

for i, v in enumerate(list):
    print ('index = %s, value = %s' % (i, v))

print (max(list))
#'a'
print (min(list))
#1

备注：

reverse操作是按照输入顺序倒序；sort操作是按照先数字从小到大，再按照字母序从小到大排序

 

样例题代码：

    n, k = map(int, input().split())
    #print ('n =', n, end = '\n')
    #print ('k =', k, end = '\n')
    x = map(int, input().split())
    #print ('x =', x)
    ans = []
    for i in x:
    	if i not in ans:
    		if len(ans) == k:
    		#delete last one
    			del ans[-1]
    		#ans.append(i)
    		ans.insert(0, i)
    		#print (ans)
    print (len(ans))
    for i in range(0, len(ans) - 1):
    	print (ans[i], end = ' ')
    print (ans[-1])