Example 1
Input
aabcbcdbca
Output
4
Distinct characters are {a,b,c,d}. Smallest window that contains them all is "dbca" with length 4.
Full lesson preview
Find the smallest substring containing all distinct characters
Given a string, find the length of the smallest substring that contains all distinct characters present in the original string.
Python practice15 minStrings – Sliding Window & FrequencyIntermediateLast updated March 25, 2026
Problem statement
You are given a string s. Determine the length of the smallest contiguous substring of s that contains every distinct character that appears anywhere in s. If the input string is empty, return 0.
For example, if s = "aabcbcdbca", the distinct characters in s are {a, b, c, d}. The smallest substring that contains all four is "dbca" which has length 4. Your function should return the length of such a substring.
Task
Use the sliding window and frequency counting to find the minimum-length window that contains every unique character from the full string.
Examples
Input format
A single string s.
Output format
An integer representing the length of the smallest substring containing all distinct characters from s. Return 0 for an empty string.
Constraints
- 0 <= len(s) <= 10^5
- s may contain arbitrary characters (letters, digits, punctuation). Solution should be O(n) time and O(m) space where m is the size of the charset encountered.
Samples
Sample 1
Input
aabcbcdbca
Output
4
Distinct characters are {a,b,c,d}. Smallest window length containing them all is 4.