Longest Consecutive Sequence in an Unsorted Array [duplicate]

Answer 1

Here is the implementation:

static int[] F(int[] A)
{
    Dictionary low = new Dictionary();
    Dictionary high = new Dictionary();

    foreach (int a in A)
    {
        int lowLength, highLength;

        bool lowIn = low.TryGetValue(a + 1, out lowLength);
        bool highIn = high.TryGetValue(a - 1, out highLength);

        if (lowIn)
        {
            if (highIn)
            {
                low.Remove(a + 1);
                high.Remove(a - 1);
                low[a - highLength] = high[a + lowLength] = lowLength + highLength + 1;
            }
            else
            {
                low.Remove(a + 1);
                low[a] = high[a + lowLength] = lowLength + 1;
            }
        }
        else
        {
            if (highIn)
            {
                high.Remove(a - 1);
                high[a] = low[a - highLength] = highLength + 1;
            }
            else
            {
                high[a] = low[a] = 1;
            }
        }
    }

    int maxLow = 0, maxLength = 0;
    foreach (var pair in low)
    {
        if (pair.Value > maxLength)
        {
            maxLength = pair.Value;
            maxLow = pair.Key;
        }
    }

    int[] ret = new int[maxLength];
    for (int i = 0; i < maxLength; i++)
    {
        ret[i] = maxLow + i;
    }

    return ret;
}