19C - Deletion of Repeats - CodeForces Solution

import sys
n=int(input())
a=list(map(int,input().split()))
M=10**9+1
g={}
for i in range(n):
    g[a[i]]=g.get(a[i],[])+[i]
p=[1]
for i in range(n):
    p+=[hash(M*p[-1])]
h=[0]*(n+1)
for i in range(n):
    h[i+1]=hash(h[i]*M+a[i])
gh=lambda k,l:hash(h[k+l]-h[k]*p[l])%sys.hash_info.modulus
i,t=0,0
while i < n:
    for j in g[a[i]]:
        if j <= i:
            continue
        w=j-i
        if j+w<=n and gh(i,w)==gh(j,w):
            i=j-1
            t=max(t,j)
            break
    i+=1
r=a[t:]
print(len(r))
print(*r)