def labelOfCluster(labelList, clusts, c):
    """
    Inputs:
        labelList: (N,) list, each is a LabelHelper object
        clusts: (K,) list of set (each set is a cluster)
        c: scalar, cluster index

    Return:
        labelObj of (any) observations in cluster c.

    Runtime:
        O(1)
    """
    return labelList[next(iter(clusts[c]))]