Simple triangle enumeration julia

triangles.jl

using SparseArrays

function find_triangles(A::SparseMatrixCSC{Int64,Int64})
    n = size(A, 1)  # number of nodes
    d = vec(sum(A, dims=2))  # degree vector
    deg_order = zeros(Int64, n)
    deg_order[sortperm(d)] = 1:n
    triangles = []
    for i = 1:n
        N_i = findnz(A[:, i])[1]  # neighbors of node i
	# only look over pairs of neighbors with higher degree order
	N_i_keep = [j for j in N_i if deg_order[j] > deg_order[i]]
        for jj = 1:length(N_i_keep)
            for kk = (jj + 1):length(N_i_keep)
                j = N_i_keep[jj]
                k = N_i_keep[kk]
                # check for triangle
		if A[j, k] > 0
                    # triangle (i, j, k)
		    push!(triangles, (i, j, k))
                end
            end
        end
    end
    return triangles
end