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.
  4. 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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    Output:

    hello
    

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

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