Given a string str and an integer K, the task is to find the length of the longest sub-string S such that every character in S appears at least K times.
Examples:
Input: str = “aabbba”, K = 3
Output: 6
Explanation:
In substring aabbba, each character repeats at least k times and its length is 6.Input: str = “ababacb”, K = 3
Output: 0
Explanation:
There is no substring where each character repeats at least k times.
Naive Approach: We have discussed the Naive Approach in the previous post.
Approach: In this post, we will discuss the approach using Divide and Conquer technique and Recursion. Below are the steps:
- Store the frequency of each characters of the given string in a frequency array of size 26.
- Initialize two variables start with 0 and end which is the length of the string str.
- Iterate over the string from start to end and count the number of times each character repeats and store it in an array.
- If any character repeats less than K times, then Divide the string into two halves. If i is the index of the string where we found that the string[i] repeats less than K times, then we divide the string into two halves from start to i and i + 1 to end.
- Recursively call for the two halves in the above steps i.e., from start to i and i + 1 to end separately and repeat the Step 2 and 3 and return the maximum of the two values reutnr by the above recursive call.
- If all the characters between start and end is repeated at least K times, then the answer is end – start.
- Largest substring with same Characters
- Largest sub-string where all the characters appear at least K times
- Find if a given string can be represented from a substring by iterating the substring “n” times
- Length of the largest substring which have character with frequency greater than or equal to half of the substring
- Longest substring with atmost K characters from the given set of characters
- Minimum number of times A has to be repeated such that B is a substring of it
- Maximum number of times str1 appears as a non-overlapping substring in str2
- Remove characters that appear more than k times
- Maximum length substring having all same characters after k changes
- Length of longest substring having all characters as K
- Longest substring such that no three consecutive characters are same
- Count distinct substrings that contain some characters at most k times
- Remove characters from a String that appears exactly K times
- Minimum length substring with exactly K distinct characters
- Find the String having each substring with exactly K distinct characters
- Searching characters and substring in a String in Java
- Longest substring of only 4's from the first N characters of the infinite string
- Minimum characters to be replaced to remove the given substring
- Length of the longest substring without repeating characters
- Print Longest substring without repeating characters
Below is the implementation of above approach:
C++
// 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; } |
Java
// Java program for the above approach import java.util.*; class GFG{ // Function to find the longest subString static 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[] = new int[26]; // Store the frequency from s[start...end] for(int i = start; i < end; i++) { count[s.charAt(i) - 'a'] += 1; } // Iterate from [start, end] for(int i = start; i < end; i++) { if (count[s.charAt(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 Math.max(left, right); } } // If all the characters are repeated // at least k times return end - start; } // Driver Code public static void main(String[] args) { // Given String str String str = "aabbba"; int k = 3; // Function Call System.out.print(longestSubString(0, str.length(), str, k) + "\n"); } } // This code is contributed by Amit Katiyar |
6
Time Complexity: O(N*log2N)
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Improved By : amit143katiyar
