please suggest efficient solution.

I am assuming that you want to generate distinct substrings of a string.

U could do this using trie in O(N^2)

Just insert all suffix of the string in trie,and then count the number of nodes is trie.To get the strings u can do dfs.

lets say abba

Suffix-abba,bba,ba,a

Insert

```
Root
/ \
a. b
/ \
b. b
/ \
b. a
/
```

a

```
Ans 7
a,ab,abb,abba,b,bb,bba
```

Edit:- Sorry i misread the question.If the substring can have only unique characters then u can do simple bruteforce as @ayushkapadia said.

If you want to generate substrings which have only unique characters, then it is very simple done in O (N X 26). As the length of that substring will not be greater than 26 according to pegion hole principle. So just do the brute force that is for every i loop over all j greater than i, but stop whenever you see a repeated character.I am not considering printing time here.But in the worst case it will be O (26 X 26 X N).

```
for i in range (0,n):
myDict = dict ()
for j in range (i,n):
if s [j] in myDict:
break
myDict[s [j]] = 1
print s [i:j+1]
```

Oohk I think i misread the question.

Thanks for correcting.