Ositus

from array import array

string = input()
length = len(string)

symbols = {string[0]: 0}

index_of_preceding = array('l', [-1] * length)

number_for_symbol = array('l', [1] * length)


rightest_ntl = str()


prime_modulus = 1000000007
    

def extra(x, y):
    global index_of_preceding
    global number_for_symbol

    index_of_rightest_ntl = -1

    for i in range(x + 1, y):
        if index_of_preceding[i] > index_of_rightest_ntl:
            index_of_rightest_ntl = index_of_preceding[i]



    if index_of_rightest_ntl > x:
        return 0
    elif index_of_rightest_ntl == -1:
        return number_for_symbol[x]
    else:
        return number_for_symbol[x] - extra(index_of_rightest_ntl, x + 1)

            

 
start = length

for i in range(1, length):
    if string[i] in symbols:
        index_of_preceding[i] = symbols[string[i]]
        number_for_symbol[i] = 2 ** i - number_for_symbol[index_of_preceding[i]]
        symbols[string[i]] = i

        rightest_ntl = string[i]
        start = i + 1
        break
        
    else:
        number_for_symbol[i] = 2 ** i
        symbols[string[i]] = i

        

        
for i in range(start, length):

            
    if string[i] in symbols:
    

        index_of_preceding[i] = symbols[string[i]]
        number_for_symbol[i] = 2 * number_for_symbol[i - 1] - extra(index_of_preceding[i], i)
        rightest_ntl = string[i]
            
        symbols[string[i]] = i
        if not 0 <= number_for_symbol[i] < prime_modulus:
            number_for_symbol[i] %= prime_modulus
            
    else:   

        number_for_symbol[i] = 2 * number_for_symbol[i - 1]
        symbols[string[i]] = i
        
        if number_for_symbol[i] >= prime_modulus:
            number_for_symbol[i] %= prime_modulus


            
print(number_for_symbol[length - 1])

Test 1

Group: 1, 2, 3

Verdict: ACCEPTED

Test 2

Group: 1, 2, 3

Verdict: ACCEPTED

Test 3

Group: 1, 2, 3

Verdict: ACCEPTED

Test 4

Group: 1, 2, 3

Verdict: ACCEPTED

Test 5

Group: 2, 3

Verdict: ACCEPTED

Test 6

Group: 3

Verdict: ACCEPTED

Test 7

Group: 3

Verdict: ACCEPTED