""" (c) http://stackoverflow.com/a/15970880
var A = new int[] {4, 5, 1, 5, 7, 6, 8, 4, 1};
var D = new Dictionary<int, HashSet<int>>();
 
foreach(int n in A)
{
    if(D.ContainsKey(n-1) && D.ContainsKey(n+1))
    {
        D[n-1].UnionWith(D[n+1]);
        D[n+1] = D[n] = D[n-1];
    }
    else if(D.ContainsKey(n-1))
    {
        D[n] = D[n-1];
    }
    else if(D.ContainsKey(n+1))
    {
        D[n] = D[n+1];
    }
    else if(!D.ContainsKey(n))
    {
        D.Add(n, new HashSet<int>());
    }
 
    D[n].Add(n);
}
 
int result = int.MinValue;
foreach(HashSet<int> H in D.Values)
{
    if(H.Count > result)
    {
        result = H.Count;
    }
}
"""
import random
 
def find_some_set(A):
    D = {} # mapping: n -> set
    for n in A:
        if (n-1) in D and (n+1) in D: # O(1), worst case O(N)
            D[n-1] |= D[n+1] # union: w.c. O(len(D[n-1]) + len(D[n+1])) = O(N)
            D[n+1] = D[n] = D[n-1]
        elif (n-1) in D:
            D[n] = D[n-1]
        elif (n+1) in D:
            D[n] = D[n+1]
        elif n not in D:
            D[n] = set()
        D[n].add(n) # O(1), w.c. O(N)
 
    return max(D.values(), key=len) # O(N)
 
def random_seq(N, randint=random.randint):
    return [randint(0, N**3) for _ in range(N)]
 
def allsame_seq(N, randint=random.randint):
    return [randint(0, N**3)] * N
 
def range_seq(N):
    return list(range(N))
 
 
if __name__ == "__main__":
    result_set = find_some_set([10, 5, 3, 1, 4, 2, 8, 7, 0])
    print(len(result_set), result_set)

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