How to resolve the algorithm Selectively replace multiple instances of a character within a string step by step in the Java programming language

Published on 12 May 2024 09:40 PM

How to resolve the algorithm Selectively replace multiple instances of a character within a string step by step in the Java programming language

Table of Contents

Problem Statement

This is admittedly a trivial task but I thought it would be interesting to see how succinctly (or otherwise) different languages can handle it. Given the string: "abracadabra", replace programatically:

Note that there is no replacement for the third 'a', second 'b' or first 'r'. The answer should, of course, be : "AErBcadCbFD".

Let's start with the solution:

Step by Step solution about How to resolve the algorithm Selectively replace multiple instances of a character within a string step by step in the Java programming language

Problem: The goal of the code is to selectively replace specific characters in a string based on their position and the provided replacement characters.

Implementation:

1. findNth Method:

  • This method takes three parameters: a string s, a character c, and an integer n.
  • It returns the index of the nth occurrence of character c in string s.
  • It recursively calls itself, reducing n by 1 and using the previous result as the starting index for the next search.

2. selectiveReplace Method:

  • This method takes two parameters: a string s and an array of Set objects (ops).
  • It converts the string s into a character array chars.
  • It iterates through each Set object in the ops array.
  • For each Set, it uses the findNth method to find the index of the nth occurrence of the old character in the string s.
  • It then replaces the character at that index with the rep character from the Set.
  • Finally, it returns a new string created from the modified chars array.

Usage: The code demonstrates the usage of the selectiveReplace method by applying it to the string "abracadabra" with the following replacement operations:

  • Replace the first occurrence of 'a' with 'A'.
  • Replace the second occurrence of 'a' with 'B'.
  • Replace the fourth occurrence of 'a' with 'C'.
  • Replace the fifth occurrence of 'a' with 'D'.
  • Replace the first occurrence of 'b' with 'E'.
  • Replace the second occurrence of 'r' with 'F'.

Output: The output of the code would be the following string: "ABraCADaEFa".

Source code in the java programming language

int findNth(String s, char c, int n) {
    if (n == 1) return s.indexOf(c);
    return s.indexOf(c, findNth(s, c, n - 1) + 1);
}

String selectiveReplace(String s, Set... ops) {
    char[] chars = s.toCharArray();
    for (Set set : ops)
        chars[findNth(s, set.old, set.n)] = set.rep;
    return new String(chars);
}

record Set(int n, char old, char rep) { }


selectiveReplace("abracadabra",
    new Set(1, 'a', 'A'),
    new Set(2, 'a', 'B'),
    new Set(4, 'a', 'C'),
    new Set(5, 'a', 'D'),
    new Set(1, 'b', 'E'),
    new Set(2, 'r', 'F'));


  

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