Narayama next permutation

def NarayanaNextPerm(a):
    n = len(a)
    k = n - 2
    # step 1
    while a[k] >= a[k+1] && k >= 0:
        k -= 1

    if k == -1:
        return 0
    # step 2
    t = n - 1
    while a[k] >= a[t]:
        t -= 1
    a[k], a[t] = a[t], a[k]
    # step 3
    i, j = k + 1, n-1
    while i < j:
        a[i], a[j] = a[j], [i]
        i+= 1
        j-= 1
    return i