def next_permutation(a): """Generate the lexicographically next permutation inplace. https://en.wikipedia.org/wiki/Permutation#Generation_in_lexicographic_order Return false if there is no next permutation. """ # Find the largest index i such that a[i] < a[i + 1]. If no such # index exists, the permutation is the last permutation for i in reversed(range(len(a) - 1)): if a[i] < a[i + 1]: break # found else: # no break: not found return False # no next permutation # Find the largest index j greater than i such that a[i] < a[j] j = next(j for j in reversed(range(i + 1, len(a))) if a[i] < a[j]) # Swap the value of a[i] with that of a[j] a[i], a[j] = a[j], a[i] # Reverse sequence from a[i + 1] up to and including the final element a[n] a[i + 1:] = reversed(a[i + 1:]) return True def perm_to_str(a): return ''.join(map(str, a)) def str_to_perm(s): return [int(c) for c in s] t = [0,1,2,3] perm_to_idx = dict() def bbin(x): return bin(x)[2:] cnt = 23 while True: perm_to_idx[perm_to_str(t)] = cnt cnt -= 1 if not next_permutation(t): break for p in perm_to_idx.keys(): for i in range(4): t = str_to_perm(p) for j in range(4): if t[j] > t[i]: t[j] -= 1 t[i] = 3 print(p, 'x', i, '->', perm_to_str(t), ':\t', bbin(perm_to_idx[p]), '\t', bbin(i), '\t', bbin(perm_to_idx[perm_to_str(t)]), end='\t') print(perm_to_idx[p], '\t', i, '\t', perm_to_idx[perm_to_str(t)]) print('\n-----\n') for p in perm_to_idx.keys(): for i in range(4): t = str_to_perm(p) for j in range(4): if t[j] > t[i]: t[j] -= 1 t[i] = 3 print(p, 'x', i, '->', perm_to_str(t), ':\t', bbin(perm_to_idx[p]), '\t', bbin(i), '\t', bbin(perm_to_idx[perm_to_str(t)]), end='\t') print(perm_to_idx[p], '\t', i, '\t', perm_to_idx[perm_to_str(t)])