Minimum replacements such that no palindromic substring of length exceeding 1 is present in the given string
Given a string str consisting of lowercase characters, the task is to modify the string such that it does not contain any palindromic substring of length exceeding 1 by minimum replacement of characters.
Examples:
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Input: str = “bbbbbbb”
Output: 4
String can be modified to “bacbacb” by replacing 4 characters.Input: str = “geeksforgeeks”
Output: 2
Approach:
To solve the problem, the idea is that, if there exists a palindrome of length larger than 3, then there exists a palindrome of length 2 or 3. Therefore, greedily remove all palindromes of length 2 or 3. Follow the steps below to solve the problem:
- Initialize a variable, say change, to store the required number of replacements.
- Iterate over the characters of the given string and perform the following steps:
- If the character at the current index is the same as the character at the next index, then increment change by 1.
- Otherwise, check if the character at the previous index is the same as the character at the next index, i.e. there is a palindromic substring of length 3. Therefore, increment change by 1.
Below is the implementation of the above approach:
C++
// C++ Program to implement// the above approach#include <bits/stdc++.h>using namespace std;// Function to count the changes required such// that no palindromic substring of length// exceeding 1 is present in the stringint maxChange(string str){ // Base Case if (str.size() <= 1) { return 0; } // Stores the count int minChanges = 0; // Iterate over the string for (int i = 0; i < str.size() - 1; i++) { // Palindromic Substring of Length 2 if (str[i] == str[i + 1]) { // Replace the next character str[i + 1] = 'N'; // Increment changes minChanges += 1; } // Palindromic Substring of Length 3 else if (i > 0 && str[i - 1] == str[i + 1]) { // Replace the next character str[i + 1] = 'N'; // Increment changes minChanges += 1; } } return minChanges;}// Driver Codeint main(){ string str = "bbbbbbb"; cout << maxChange(str); return 0;} |
Java
// Java Program to implement// the above approachimport java.util.*;class GFG{// Function to count the changes required such// that no palindromic subString of length// exceeding 1 is present in the Stringstatic int maxChange(char []str){ // Base Case if (str.length <= 1) { return 0; } // Stores the count int minChanges = 0; // Iterate over the String for (int i = 0; i < str.length - 1; i++) { // Palindromic SubString of Length 2 if (str[i] == str[i + 1]) { // Replace the next character str[i + 1] = 'N'; // Increment changes minChanges += 1; } // Palindromic SubString of Length 3 else if (i > 0 && str[i - 1] == str[i + 1]) { // Replace the next character str[i + 1] = 'N'; // Increment changes minChanges += 1; } } return minChanges;}// Driver Codepublic static void main(String[] args){ String str = "bbbbbbb"; System.out.print(maxChange(str.toCharArray()));}}// This code is contributed by shikhasingrajput |
Python3
# Python3 Program to implement# the above approach# Function to count the changes required such# that no palindromic subof length# exceeding 1 is present in the stringdef maxChange(str): str = [i for i in str] if (len(str) <= 1): return 0 # Stores the count minChanges = 0 # Iterate over the string for i in range(len(str) - 1): # Palindromic Subof Length 2 if (str[i] == str[i + 1]): # Replace the next character str[i + 1] = 'N' # Increment changes minChanges += 1 # Palindromic Subof Length 3 elif (i > 0 and str[i - 1] == str[i + 1]): # Replace the next character str[i + 1] = 'N' # Increment changes minChanges += 1 return minChanges# Driver Codeif __name__ == '__main__': str = "bbbbbbb" print (maxChange(str))# This code is contributed by mohit kumar 29. |
C#
// C# Program to implement// the above approachusing System;public class GFG{// Function to count the changes required such// that no palindromic subString of length// exceeding 1 is present in the Stringstatic int maxChange(char []str){ // Base Case if (str.Length <= 1) { return 0; } // Stores the count int minChanges = 0; // Iterate over the String for (int i = 0; i < str.Length - 1; i++) { // Palindromic SubString of Length 2 if (str[i] == str[i + 1]) { // Replace the next character str[i + 1] = 'N'; // Increment changes minChanges += 1; } // Palindromic SubString of Length 3 else if (i > 0 && str[i - 1] == str[i + 1]) { // Replace the next character str[i + 1] = 'N'; // Increment changes minChanges += 1; } } return minChanges;}// Driver Codepublic static void Main(String[] args){ String str = "bbbbbbb"; Console.Write(maxChange(str.ToCharArray()));}} // This code contributed by shikhasingrajput |
Javascript
<script> // JavaScript Program to implement // the above approach // Function to count the changes required such // that no palindromic subString of length // exceeding 1 is present in the String function maxChange(str) { // Base Case if (str.length <= 1) { return 0; } // Stores the count var minChanges = 0; // Iterate over the String for (var i = 0; i < str.length - 1; i++) { // Palindromic SubString of Length 2 if (str[i] === str[i + 1]) { // Replace the next character str[i + 1] = "N"; // Increment changes minChanges += 1; } // Palindromic SubString of Length 3 else if (i > 0 && str[i - 1] === str[i + 1]) { // Replace the next character str[i + 1] = "N"; // Increment changes minChanges += 1; } } return minChanges; } // Driver Code var str = "bbbbbbb"; document.write(maxChange(str.split(""))); </script> |
Output:
4
Time Complexity: O(N)
Auxiliary Space: O(1)
