Replace two substrings (of a string) with each other - GeeksforGeeks

17 Dec, 2021
Given 3 strings S, A and B. The task is to replace every sub-string of S equal to A with B and every sub-string of S equal to B with A. It is possible that two or more sub-strings matching A or B overlap. To avoid confusion about this situation, you should find the leftmost sub-string that matches A or B, replace it, and then continue with the rest of the string. For example, when matching A = “aa” with S = “aaa”, A[0, 1] will be given preference over A[1, 2]. 
Note that A and B will have the same length and A != B.
Examples: 
Input: S = “aab”, A = “aa”, B = “bb” Output: bbb We match the first two characters with A and replacing it with B we get bbb. Then we continue the algorithm starting at index 3 and we don’t find any more matches.
Input: S = “aabbaabb”, A = “aa”, B = “bb” Output: bbaabbaa We replace all the occurrences of “aa” with “bb” and “bb” with “aa”, so the resultant string is “bbaabbaa”.  
Approach: Go through every possible sub-string from S of length len(A). if any sub-string matches A or B then update the string as required and print the updated string in the end.
Below is the implementation of the above approach: 
C++
Java
Python3
C#
PHP
Javascript
// C++ implementation of the approach#include<bits/stdc++.h>using namespace std; // Function to return the resultant stringstring updateString(string S,                    string A, string B){     int l = A.length();     // Iterate through all positions i    for (int i = 0; i + l <= S.length(); i++)    {         // Current sub-string of        // length = len(A) = len(B)        string curr = S.substr(i, i + l);         // If current sub-string gets        // equal to A or B        if (curr == A)        {             // Update S after replacing A            string new_string = "";            new_string += S.substr(0, i) + B +                          S.substr(i + l, S.length());            S = new_string;            i += l - 1;        }        else if(curr == B)        {             // Update S after replacing B            string new_string = "";            new_string += S.substr(0, i) + A +                          S.substr(i + l, S.length());            S = new_string;            i += l - 1;        }        else        {          //do nothing        }    }     // Return the updated string    return S;} // Driver codeint main(){    string S = "aaxb";    string A = "aa";    string B = "bb";     cout << (updateString(S, A, B)) << endl;} // This code is contributed by// Surendra_Gangwar
// Java implementation of the approachclass GFG {     // Function to return the resultant string    static String updateString(String S, String A, String B)    {         int l = A.length();         // Iterate through all positions i        for (int i = 0; i + l <= S.length(); i++) {             // Current sub-string of length = len(A) = len(B)            String curr = S.substring(i, i + l);             // If current sub-string gets equal to A or B            if (curr.equals(A)) {                 // Update S after replacing A                String new_string                    = S.substring(0, i)                      + B + S.substring(i + l, S.length());                S = new_string;                i += l - 1;            }            else {                 // Update S after replacing B                String new_string                    = S.substring(0, i)                      + A + S.substring(i + l, S.length());                S = new_string;                i += l - 1;            }        }         // Return the updated string        return S;    }     // Driver code    public static void main(String[] args)    {        String S = "aab";        String A = "aa";        String B = "bb";         System.out.println(updateString(S, A, B));    }}
# Python3 implementation of the approach # Function to return the resultant stringdef updateString(S, A, B):         l = len(A)         # Iterate through all positions i    i = 0    while i + l <= len(S):         # Current sub-string of        # length = len(A) = len(B)        curr = S[i:i+l]         # If current sub-string gets        # equal to A or B        if curr == A:             # Update S after replacing A            new_string = S[0:i] + B + S[i + l:len(S)]            S = new_string            i += l - 1                     else:             # Update S after replacing B            new_string = S[0:i] + A + S[i + l:len(S)]            S = new_string            i += l - 1                 i += 1         # Return the updated string    return S # Driver codeif __name__ == "__main__":         S = "aab"    A = "aa"    B = "bb"     print(updateString(S, A, B))     # This code is contributed by Rituraj Jain
// C# implementation of the approachusing System; class GFG{     // Function to return the resultant string    static string updateString(string S, string A, string B)    {        int l = A.Length;         // Iterate through all positions i        for (int i = 0; i + l <= S.Length; i++)        {             // Current sub-string of length = len(A) = len(B)            string curr = S.Substring(i, l);             // If current sub-string gets equal to A or B            if (curr.Equals(A))            {                 // Update S after replacing A                string new_string = S.Substring(0, i) +                                 B + S.Substring(i + l);                S = new_string;                i += l - 1;            }            else            {                 // Update S after replacing B                string new_string = S.Substring(0, i) +                                A + S.Substring(i + l);                S = new_string;                i += l - 1;            }        }         // Return the updated string        return S;    }     // Driver code    public static void Main()    {        string S = "aab";        string A = "aa";        string B = "bb";        Console.WriteLine(updateString(S, A, B));    }} // This code is contributed by Ryuga
<?php// PHP implementation of the approach// Function to return the resultant stringfunction updateString($S, $A, $B){     $l = strlen($A);     // Iterate through all positions i    for ($i = 0; $i + $l <= strlen($S); $i++)    {         // Current sub-string of length = len(A) = len(B)        $curr = substr($S, $i, $i + $l);         // If current sub-string gets equal to A or B        if (strcmp($curr, $A) == 0)        {             // Update S after replacing A            $new_string = substr($S, 0, $i) . $B .                        substr($S, $i + $l, strlen($S));            $S = $new_string;            $i += $l - 1;        }        else        {             // Update S after replacing B            $new_string = substr($S, 0, $i) . $A .                        substr($S, $i + $l, strlen($S));            $S = $new_string;            $i += $l - 1;        }    }     // Return the updated string    return $S;} // Driver code$S = "aab";$A = "aa";$B = "bb"; echo(updateString($S, $A, $B)); // This code is contributed by Code_Mech.
<script> // Javascript implementation of the approach // Function to return the resultant stringfunction updateString(S, A, B){    let l = A.length;     // Iterate through all positions i    for(let i = 0; i + l <= S.length; i++)    {                 // Current sub-string of length = len(A) = len(B)        let curr = S.substring(i, i + l);         // If current sub-string gets equal to A or B        if (curr == A)        {                         // Update S after replacing A            let new_string = S.substring(0, i) +                         B + S.substring(i + l);            S = new_string;            i += l - 1;        }        else        {                         // Update S after replacing B            let new_string = S.substring(0, i) +                         A + S.substring(i + l);            S = new_string;            i += l - 1;        }    }     // Return the updated string    return S;} // Driver codelet S = "aab";let A = "aa";let B = "bb"; document.write(updateString(S, A, B)); // This code is contributed by mukesh07 </script>
bbb
 
ankthon
rituraj_jain
SURENDRA_GANGWAR
Code_Mech
mukesh07
shobhittewari
substring
Pattern Searching
Strings
Strings
Pattern Searching
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