Skip to content

# Change the given string according to the given conditions

• Last Updated : 08 Nov, 2021

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

Examples:

Attention reader! Don’t stop learning now. Get hold of all the important DSA concepts with the DSA Self Paced Course at a student-friendly price and become industry ready.  To complete your preparation from learning a language to DS Algo and many more,  please refer Complete Interview Preparation Course.

In case you wish to attend live classes with experts, please refer DSA Live Classes for Working Professionals and Competitive Programming Live for Students.

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

 `// C++ program for the above approach` `#include ``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 = ``"hello"``;` `    ``// Function Call``    ``cout << proofreadSpell(str);``}`

## Java

 `// Java program for the above approach``import` `java.util.*;` `class` `GFG{``    ` `// Function to proofread the spells``public` `static` `String proofreadSpell(String str)``{``    ``Vector result = ``new` `Vector();` `    ``// 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 = ``"hello"``;` `    ``// Function call``    ``System.out.println(proofreadSpell(str));``}``}` `// This code is contributed by divyeshrabadiya07`

## Python3

 `# Python3 program for``# the above approach` `# Function to proofread``# the spells``def` `proofreadSpell(``str``):``  ` `    ``result ``=` `[]` `    ``# Loop to iterate over the``    ``# characters of the string``    ``for` `c ``in` `str``:` `        ``# Push the current character c``        ``# in the stack``        ``result.append(c)``        ``n ``=` `len``(result)` `        ``# Check for Rule 1``        ``if``(n >``=` `3``):``            ``if``(result[n ``-` `1``] ``=``=` `result[n ``-` `2``] ``and``               ``result[n ``-` `1``] ``=``=` `result[n ``-` `3``]):``                ``result.pop()``        ``n ``=` `len``(result)` `        ``# Check for Rule 2``        ``if``(n >``=` `4``):``            ``if``(result[n ``-` `1``] ``=``=` `result[n ``-` `2``] ``and``               ``result[n ``-` `3``] ``=``=` `result[n ``-` `4``]):``                ``result.pop()` `    ``# To store the``    ``# resultant string``    ``resultStr ``=` `""` `    ``# Loop to iterate over the``    ``# characters of stack``    ``for` `c ``in` `result:``        ``resultStr ``+``=` `c` `    ``# Return the resultant string``    ``return` `resultStr` `# Driver Code` `# Given string str``str` `=` `"hello"` `# Function Call``print``(proofreadSpell(``str``))` `# This code is contributed by avanitrachhadiya2155`

## C#

 `// 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 = ``"hello"``;` `    ``// Function call``    ``Console.Write(proofreadSpell(str));``}``}` `// This code is contributed by rutvik_56`

## Javascript

 ``
Output:
`hello`

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

My Personal Notes arrow_drop_up