Python permutation using backtracking -


i'm trying learn permutation using backtracking. i've written following code stops after first output. 

def permutations(str_in, sofar):      if len(str_in) != 0:         c in str_in:             sofar.append(c)             temp_str = str_in             temp_str.remove(c)             print temp_str, sofar             permutations(temp_str, sofar)     else:         print sofar  inp = "abcd"         str_in = list(inp) permutations(str_in, [])

this output i'm getting this:

['b', 'c', 'd'] ['a'] ['c', 'd'] ['a', 'b'] ['d'] ['a', 'b', 'c'] [] ['a', 'b', 'c', 'd'] ['a', 'b', 'c', 'd']

i'm sure simple, i'm not able understand mistake i'm making here.

here geeksforgeeks method, bhavya jain, of permuting string. missing logic in code recursive step on sublists , swapping behavior. here visualization.

geeksforgeeks visualization of recursive steps

def permute(a, l, r):     if l==r:         print tostring(a)     else:         in xrange(l,r+1):             a[l], a[i] = a[i], a[l]             permute(a, l+1, r)             a[l], a[i] = a[i], a[l] # backtrack  # driver program test above function string = "abc" n = len(string) = list(string) permute(a, 0, n-1)

output

['a', 'b', 'c'] ['a', 'c', 'b'] ['b', 'a', 'c'] ['b', 'c', 'a'] ['c', 'b', 'a'] ['c', 'a', 'b']

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