Change the given string according to the given conditions

Given a string S, the task is to change the string id it doesn’t follow any of the rules given below and print the updated string. The rules for the proofreading are:

  1. If there are three consecutive characters, then its a wrong spell. Remove one of the character. For Example: string “ooops” can be change to “oops”.
  2. If two pairs of same character (AABB) are connected together, it’s a wrong spell. Delete one of the character of the second pair.For Example: string “helloo” can be changed to “hello”.
  3. The rules follow the priority from left to right.

Examples:

Input: S = “helloo”
Output: hello
Explanation:
As per the Rule #2
helloo => hello

Input: S = “woooow”
Output: woow
Explanation: 
As per the Rule #2
woooow => wooow
As per the Rule #1
wooow => woow

Approach: The idea is to traverse the string and if there is a wrong spelling, remove the extra characters according to the given conditions. As the priority of errors is from left to right, and according to the rules given, it can be seen that the judgment of spelling errors will not conflict. Consider traversing from left to right, adding the already legal characters to the result. Below are the steps:



  • Initialize a stack to store the characters and to compare the last characters of the string.
  • Traverse the string and add the character to the stack.
  • Check the last 3 characters of the stack, if the same then pop the character at the top of the stack.
  • Check the last 4 characters of the stack, if the same then pop the character at the top of the stack.
  • Finally return the characters of the stack.

Below is the implementation of the above approach:

C++

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// C++ program for the above approach
  
#include <bits/stdc++.h>
using namespace std;
  
// Function to proofread the spells
string proofreadSpell(string& str)
{
    vector<char> result;
  
    // Loop to iterate over the
    // characters of the string
    for (char c : str) {
  
        // Push the current character c
        // in the stack
        result.push_back(c);
  
        int n = result.size();
  
        // Check for Rule 1
        if (n >= 3) {
            if (result[n - 1]
                    == result[n - 2]
                && result[n - 1]
                       == result[n - 3]) {
                result.pop_back();
            }
        }
        n = result.size();
  
        // Check for Rule 2
        if (n >= 4) {
            if (result[n - 1]
                    == result[n - 2]
                && result[n - 3]
                       == result[n - 4]) {
                result.pop_back();
            }
        }
    }
  
    // To store the resultant string
    string resultStr = "";
  
    // Loop to iterate over the
    // characters of stack
    for (char c : result) {
        resultStr += c;
    }
  
    // Return the resultant string
    return resultStr;
}
  
// Driver Code
int main()
{
    // Given string str
    string str = "helloo";
  
    // Function Call
    cout << proofreadSpell(str);
}

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Java

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// Java program for the above approach 
import java.util.*;
  
class GFG{
      
// Function to proofread the spells 
public static String proofreadSpell(String str) 
    Vector<Character> result = new Vector<Character>(); 
  
    // Loop to iterate over the 
    // characters of the string 
    for(int i = 0; i < str.length(); i++) 
    
          
        // Push the current character c 
        // in the stack 
        result.add(str.charAt(i)); 
  
        int n = result.size(); 
  
        // Check for Rule 1 
        if (n >= 3
        
            if (result.get(n - 1) == 
                result.get(n - 2) && 
                result.get(n - 1) == 
                result.get(n - 3))
            
                result.remove(result.size() - 1); 
            
        
        n = result.size(); 
  
        // Check for Rule 2 
        if (n >= 4
        
            if (result.get(n - 1) == 
                result.get(n - 2) && 
                result.get(n - 3) == 
                result.get(n - 4))
            
                result.remove(result.size() - 1); 
            
        
    
  
    // To store the resultant string 
    String resultStr = ""
  
    // Loop to iterate over the 
    // characters of stack 
    for(Character c : result)
    
        resultStr += c; 
    
      
    // Return the resultant string 
    return resultStr; 
}
  
// Driver Code
public static void main(String[] args)
{
      
    // Given string str 
    String str = "helloo"
  
    // Function call 
    System.out.println(proofreadSpell(str));
}
}
  
// This code is contributed by divyeshrabadiya07

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C#

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// C# program for the above approach  
using System;
using System.Collections; 
using System.Collections.Generic;
  
class GFG{
  
// Function to proofread the spells
static string proofreadSpell(string str)
{
      
    // ArrayList result=new ArrayList();
    List<char> result = new List<char>();
      
    // Loop to iterate over the
    // characters of the string
    foreach(char c in str)
    {
  
        // Push the current character c
        // in the stack
        result.Add(c);
  
        int n = result.Count;
  
        // Check for Rule 1
        if (n >= 3) 
        {
            if (result[n - 1] == result[n - 2] && 
                result[n - 1] == result[n - 3])
            {
                result.RemoveAt(n - 1);
            }
        }
          
        n = result.Count;
  
        // Check for Rule 2
        if (n >= 4) 
        {
            if (result[n - 1] == result[n - 2] && 
                result[n - 3] == result[n - 4]) 
            {
                result.RemoveAt(n - 1);
            }
        }
    }
  
    // To store the resultant string
    string resultStr = "";
  
    // Loop to iterate over the
    // characters of stack
    foreach(char c in result)
    {
        resultStr += c;
    }
  
    // Return the resultant string
    return resultStr;
}
  
// Driver code
public static void Main(string[] args)
{
      
    // Given string str
    string str = "helloo";
  
    // Function call
    Console.Write(proofreadSpell(str));
}
}
  
// This code is contributed by rutvik_56

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Output:

hello

Time Complexity: O(N)
Auxiliary Space: O(N)

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