“…Recently, deep hashing methods [47,22] have shown great improvements over conventional hashing methods [45,14,15,21,35,36,18]. Furthermore, deep hashing methods can be grouped by how the similarity of the learned hashing codes are measured, namely pointwise [48,53,39,11,49], pairwise [24,22,4,3], triplet-wise [44,31], or listwise [51]. Among them, pointwise methods have a O(N ) computational complexity, whilst the complexity of the others are of at least O(N 2 ) for N data points.…”