Largest substring where all characters appear at least K times | Set 2

// C++ program for the above approach 
#include <bits/stdc++.h> 
using namespace std; 

// Function to find the longest substring 
int longestSubstring(int start, int end, 
                    string s, int k) 
{ 
    int left, right; 

    // Array for counting the number of 
    // times each character repeats 
    // count the number of times each 
    // character repeats from start to end 
    int count[26] = { 0 }; 

    // Store the frequency from s[start...end] 
    for (int i = start; i < end; i++) { 
        count[s[i] - 'a'] += 1; 
    } 

    // Iterate from [start, end] 
    for (int i = start; i < end; i++) { 

        if (count[s[i] - 'a'] < k) { 

            // Recursive call for left subpart 
            left = longestSubstring(start, 
                                    i, 
                                    s, 
                                    k); 

            // Recursive call for right subpart 
            right = longestSubstring(i + 1, 
                                    end, 
                                    s, 
                                    k); 

            // Return maximum of left & right 
            return max(left, right); 
        } 
    } 

    // If all the characters are repeated 
    // at least k times 
    return end - start; 
} 

// Driver Code 
int main() 
{ 
    // Given String str 
    string str = "aabbba"; 
    int k = 3; 

    // Function Call 
    cout << longestSubstring(0, str.length(), 
                            str, k) 
        << endl; 
    return 0; 
}