Length of the smallest sub-string consisting of maximum distinct characters

Given a string of length N, find the length of the smallest sub-string consisting of maximum distinct characters. Note : Our output can have same character.

Examples:

Input : "AABBBCBB"
Output : 5

Input : "AABBBCBBAC"
Output : 3
Explanation : Sub-string -> "BAC"

Input : "GEEKSGEEKSFOR"
Output : 8
Explanation : Sub-string -> "GEEKSFOR"



Method 1 (Brute Force)

We can consider all sub-strings one by one and check for each sub-string both conditions together
1. sub-string’s distinct characters is equal to maximum distinct characters
2. sub-sting’s length should be minimum .
Time Complexity : O(n^3)

C++

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/* C++ program to find the length of the smallest 
substring consisting of maximum distinct characters */
#include <bits/stdc++.h>
using namespace std;
  
#define NO_OF_CHARS 256
  
// Find maximum distinct characters in any string
int max_distinct_char(string str, int n){
  
    // Initialize all character's count with 0
    int count[NO_OF_CHARS] = {0};
      
    // Increase the count in array if a character
    // is found
    for (int i = 0; i < n;  i++)
        count[str[i]]++;
      
    int max_distinct = 0;
    for (int i = 0; i < NO_OF_CHARS;  i++)
        if (count[i] != 0)      
            max_distinct++;     
      
    return max_distinct;
}
  
int smallesteSubstr_maxDistictChar(string str){
  
    int n = str.size();     // size of given string
  
    // Find maximum distinct characters in any string
    int max_distinct = max_distinct_char(str, n);
    int minl = n;   // result
      
    // Brute force approch to find all substrings
    for (int i=0 ;i<n ;i++){
        for (int j=0; j<n; j++){
            string subs =  str.substr(i,j);
            int subs_lenght = subs.size();
            int sub_distinct_char = max_distinct_char(subs, subs_lenght); 
              
            // We have to check here both conditions together
            // 1. substring's distinct characters is equal
            //    to maximum distinct characters
            // 2. substing's length should be minimum 
            if (subs_lenght < minl && max_distinct == sub_distinct_char){
                minl = subs_lenght;
            }
        }
    }
    return minl;
}
  
/* Driver program to test above function */
int main()
{
    // Input String
    string str = "AABBBCBB";
      
    int len =  smallesteSubstr_maxDistictChar(str);
    cout << " The length of the smallest substring"
            " consisting of maximum distinct "
            "characters : " << len;
    return 0;
}

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Python 3

# Python 3 program to find the length
# of the smallest substring consisting
# of maximum distinct characters
NO_OF_CHARS = 256

# Find maximum distinct characters
# in any string
def max_distinct_char(str, n):



# Initialize all character’s
# count with 0
count = [0] * NO_OF_CHARS

# Increase the count in array
# if a character is found
for i in range(n):
count[ord(str[i])] += 1

max_distinct = 0
for i in range(NO_OF_CHARS):
if (count[i] != 0):
max_distinct += 1

return max_distinct

def smallesteSubstr_maxDistictChar(str):

n = len(str) # size of given string

# Find maximum distinct characters
# in any string
max_distinct = max_distinct_char(str, n)
minl = n # result

# Brute force approch to
# find all substrings
for i in range(n):
for j in range(n):
subs = str[i:j]
subs_lenght = len(subs)
sub_distinct_char = max_distinct_char(subs,
subs_lenght)

# We have to check here both conditions together
# 1. substring’s distinct characters is equal
# to maximum distinct characters
# 2. substing’s length should be minimum
if (subs_lenght < minl and max_distinct == sub_distinct_char): minl = subs_lenght return minl # Driver Code if __name__ == "__main__": # Input String str = "AABBBCBB" l = smallesteSubstr_maxDistictChar(str); print( "The length of the smallest substring", "consisting of maximum distinct", "characters :", l) # This code is contributed by ChitraNayal [tabbyending] Output:

 The length of the smallest substring consisting
 of maximum distinct characters : 5

Method 2 (Efficient)

  1. Count all distinct characters in given string.
  2. Maintain a window of characters. Whenever the window contains all characters of given string, we shrink the window from left side to remove extra characters and then compare its length with smallest window fount so far.

Please refer Smallest window that contains all characters of string itself for implementation and more details.

Asked In : DailyHunt

This article is contributed by Harshit Agrawal. If you like GeeksforGeeks and would like to contribute, you can also write an article using contribute.geeksforgeeks.org or mail your article to contribute@geeksforgeeks.org. See your article appearing on the GeeksforGeeks main page and help other Geeks.

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Improved By : ChitraNayal