Understand Longest Repeating Character Replacement Problem

Problem Name: Longest Repeating Character Replacement
Problem Description:

Longest Repeating Character Replacement

Problem Statement:

In this problem, you are given a string s and an integer k. Your task is to find the length of the longest substring that contains the same character, where you can replace at most k characters in the string to form this substring.

Problem Explanation:

Given a string s, we need to determine the length of the longest substring where all characters are the same, with the possibility of replacing at most k characters in the string.

Approach:

The problem can be solved using the sliding window technique, where we maintain a window of characters that contains at most k different characters (the ones that we will replace). We will use the following approach:

findlength Function:

This helper function calculates the maximum length of a substring that consists entirely of the character c after replacing at most k characters in the string s.

Parameters:

  • string s: The input string.
  • int k: The maximum number of characters that can be replaced.
  • char c: The character to form the longest substring of.

Solution Steps:

  1. Initialization:

    • Start with i as the right boundary of the sliding window.
    • l is the left boundary of the sliding window.
    • cnt counts the number of characters that need to be replaced to make the substring consist entirely of c.
    • maxlength stores the maximum length of the desired substring found so far.

  2. Sliding Window Technique:

    • Iterate over the string with i as the right boundary.
    • If the character at the current position s[i] is not equal to c, increment cnt.
    • If cnt exceeds k, adjust the left boundary l until cnt is less than or equal to k.
    • Update maxlength with the length of the current valid window (i - l + 1).

  3. Return the result:

    • Return the maximum length found for the character c.

Test Cases

Test Case 1: Standard Case

Input:
s = "ABAB", k = 2

Output:
4

Explanation:
By changing the first two 'A's or the first two 'B's, we can make the entire string consist of the same character. Thus, the maximum length of the substring is 4.

Test Case 2: Case with a Large k

Input:
s = "AABABBA", k = 1

Output:
4

Explanation:
By replacing the middle 'B' with an 'A', we can form the substring "AAAA" of length 4. The maximum length is 4.

Test Case 3: No Replacement Needed

Input:
s = "BBBB", k = 2

Output:
4

Explanation:
The entire string already consists of the same character, so no replacements are needed. The maximum length is 4.

Test Case 4: Large String with One Change

Input:
s = "AABACD", k = 1

Output:
3

Explanation:
By changing one 'C' to 'A', we can form the substring "AAA" of length 3. Thus, the maximum length is 3.

Test Case 5: Multiple Characters to Replace

Input:
s = "AABBAA", k = 2

Output:
4

Explanation:
By changing the first two 'B's to 'A', we can form the substring "AAAA" of length 4. The maximum length is 4.

Category:
  • Strings
Programming Language:
  • Java
Reference Link:

https://leetcode.com/problems/longest-repeating-character-replacement/description/

Online IDE

Scroll down for output
Java
Output:
Loading component...
Loading component...
Tracking code (View only. In case you want to track the code, click this button):
Main Function:
Main Function is not defined.
Helper Function:
INPUT: s = "ABAB" , k =2
OUTPUT SENTENCE: 4
public static int characterReplacement(string s , int k){
int maxi =0;
for(int i = 0; i < 26; i++){
int temp = replacedcount(s, k , 'A' + i);
maxi = max(maxi, temp);
}
return maxi;
}//function end
Utility Functions and Global variables:
public static int replacedcount(string s, int k, char c){
int i(0), l(0) , cnt(0) , maxlength(0);
while(i < s.length()){
if(s[i] != c){
cnt++;
}
while(cnt > k){
if(s[l] != c){
cnt--;
}
l++;
}
maxlength = max(maxlength, i-l+1);
i++;
}
return maxlength;
}//function end
Privacy Policy | About