生成给定字符串的所有子字符串

Question

I want to generate all the possible substrings from a given string without redundant values as follows:

input: 'abba'

output: 'a','b','ab','ba','abb','bba'

Here is my code

s='abba' 
for i in range (0,len(s)):
    for j in range (i+1,len(s)):
        print(s[i:j])

My output is 'a','ab','abb','b','bb','b'

As you can see from the output 'b' is repeated, and 'bba' does not exist.

I want to know and learn the right logic to produce all unique substrings.

Answer 1

Fixing the indexing a bit

s='abba' 
for i in range (0,len(s)):
    for j in range (i,len(s)):
        print(s[i:(j+1)])

yields the following output

a
ab
abb
abba
b
bb
bba
b
ba
a

Basically, the indexing fix takes into account that

• 'abba'[3:3] produces just zero-length string ''

but

• 'abba'[3:4] produces string 'a' which has length one.

Duplicates you may remove by using set() , as follows:

s='abba'
ss = set()
for i in range (0,len(s)):
    for j in range (i,len(s)):
        ss.add(s[i:(j+1)])
        
print(sorted(ss))

Then you will have the following result ['a', 'ab', 'abb', 'abba', 'b', 'ba', 'bb', 'bba'] .