HardNo. 0828
Count Unique Characters of All Substrings of a Given String — LeetCode 828 Python Solution
- Pattern
- Dynamic Programming
- Topics
- Hash Table, String, Dynamic Programming
- Reading time
- 2 min
- Source
- leetcode.com
The problem
Let's define a function countUniqueChars(s) that returns the number of unique characters in s. For example, calling countUniqueChars(s) if s = "LEETCODE" then "L", "T", "C", "O", "D" are the unique characters since they appear only once in s, therefore countUniqueChars(s) = 5.
Example
- Input
- s = "ABC"
- Output
- 10
- Explanation
- All possible substrings are: "A","B","C","AB","BC" and "ABC".
Python solution
class Solution:
def uniqueLetterString(self, s: str) -> int:
d = defaultdict(list)
for i, c in enumerate(s):
d[c].append(i)
ans = 0
for v in d.values():
v = [-1] + v + [len(s)]
for i in range(1, len(v) - 1):
ans += (v[i] - v[i - 1]) * (v[i + 1] - v[i])
return ansComplexity
- Time
- O(n)
- Space · auxiliary
- O(n)
Pattern: Dynamic Programming
Define a state, write the transition, and stop recomputing the same subproblem. LeetCode 828. Count Unique Characters of All Substrings of a Given String is filed here because LeetCode tags it Dynamic Programming, which is the vocabulary this hub collects.
The dynamic programming guide has the Python template for the pattern and the 481 LeetCode problems that use it.
Related problems
| No. | Problem | Difficulty |
|---|---|---|
| 0139 | Word Break | Medium |
| 0140 | Word Break II | Hard |
| 0691 | Stickers to Spell Word | Hard |
| 0792 | Number of Matching Subsequences | Medium |
| 1048 | Longest String Chain | Medium |
| 1255 | Maximum Score Words Formed by Letters | Hard |
Frequently asked questions
- How hard is LeetCode 828. Count Unique Characters of All Substrings of a Given String?
LeetCode 828. Count Unique Characters of All Substrings of a Given String is rated Hard on LeetCode.
- What is the time complexity of LeetCode 828. Count Unique Characters of All Substrings of a Given String?
The Python solution on this page runs in O(n).
- What is the space complexity of LeetCode 828. Count Unique Characters of All Substrings of a Given String?
The Python solution on this page uses O(n) auxiliary space.
- What topics does LeetCode 828. Count Unique Characters of All Substrings of a Given String cover?
LeetCode 828. Count Unique Characters of All Substrings of a Given String is tagged Hash Table, String and Dynamic Programming on LeetCode.