test.py

def permute_all(a, l, r): 
    if l==r: 
        print("".join(a)) 
    else: 
        for i in range(l,r+1): 
            a[l], a[i] = a[i], a[l] 
            permute_all(a, l+1, r) 
            a[l], a[i] = a[i], a[l] # backtrack 
  
# Driver program to test the above function 
string = "ABC1"
permute_all(list(string), 0, len(string)-1) 

def letterCasePermutation(S: str) -> [str]:
    if S == "": return [""]
    ans = []
    if S[0].isalpha():
        for i in letterCasePermutation(S[1:len(S)]):
            print(i)
            ans.append(S[0].upper() + i)
            ans.append(S[0].lower() + i)
    else:
        for i in letterCasePermutation(S[1:len(S)]):
            ans.append(S[0] + i)
    return ans


ans = letterCasePermutation("ABC2")
print(ans)






def subsetsUtil(A, subset, index, res): 
    res.append(subset) 
    #print(subset)
    for i in range(index, len(A)):  
          
        # include the A[i] in subset.  
        subset.append(A[i]) 
          
        # move onto the next element.  
        subsetsUtil(A, list(subset), i + 1, res)  
          
        # exclude the A[i] from subset and  
        # triggers backtracking. 
        subset.pop(-1)  
    return
  
# below function returns the subsets of vector A.  
def subsets(A): 
    subset = [] 
    res = []  
    # keeps track of current element in vector A  
    index = 0
    subsetsUtil(A, subset, index, res) 
    print(res)

subsets("ABC3")


def printCombination(arr, r): 
      
    # A temporary array to  
    # store all combination 
    # one by one 
    data = [0]
  
    # Print all combination  
    # using temprary array 'data[]' 
    combinationUtil(arr, data, 0, len(arr) - 1, 0, r)
  
# arr[] ---> Input Array 
# data[] ---> Temporary array to 
#         store current combination 
# start & end ---> Staring and Ending 
#             indexes in arr[] 
# index ---> Current index in data[] 
# r ---> Size of a combination to be printed  
def combinationUtil(arr, data, start, end, index, r): 
                          
    # Current combination is ready  
    # to be printed, print it 
    if (index == r): 
        for j in range(r): 
            print(data[j], end = " ") 
        print() 
        return 
  
    # replace index with all 
    # possible elements. The 
    # condition "end-i+1 >=  
    # r-index" makes sure that  
    # including one element at 
    # index will make a combination  
    # with remaining elements at  
    # remaining positions 
    i = start;  
    while(i <= end and end - i + 1 >= r - index): 
        data[index] = arr[i]
        combinationUtil(arr, data, i + 1,  
                        end, index + 1, r) 
        i += 1

#printCombination("ABC4", 2)