# 1698 Number of Distinct Substrings in a String

Given a string `s`, return the number of distinct substrings of `s`.

A substring of a string is obtained by deleting any number of characters (possibly zero) from the front of the string and any number (possibly zero) from the back of the string.

Example 1:

``````Input: s = "aabbaba"
Output: 21
Explanation: The set of distinct strings is
["a","b","aa","bb","ab","ba","aab","abb","bab","bba","aba","aabb",
"abba","bbab","baba","aabba","abbab","bbaba","aabbab","abbaba","aabbaba"]
``````

Example 2:

``````Input: s = "abcdefg"
Output: 28
``````

Constraints:

• `1 <= s.length <= 500`
• `s` consists of lowercase English letters.

Follow up: Can you solve this problem in `O(n)` time complexity?

 `````` 1 2 3 4 5 6 7 8 9 10 11 12 13 14 `````` ``````class Solution: def countDistinct(self, s: str) -> int: subs = set() n = len(s) for i in range(n): for j in range(i+1, n+1): subs.add(s[i:j]) return len(subs) ''' Other approaches: 1. Trie 2. Rolling hash? '''``````