算法1 双指针算法

时间复杂度$O(n)$

python 代码

if __name__=="__main__":
    n = int(input())
    num = [int(i) for i in input().split()]
    dict = {}
    i,m = 0,0
    for j,x in enumerate(num):
        if x in dict:
            i = max(dict[x],i)#维护起点i
        m = max(m,j-i+1)
        dict[x] = j+1#维护字典全部从1开始算
    print(m)