Swapping Characters in a String in Java

Question

Given the above excerpt from a Java code, I need to modify the code such that it could recursively swap pairs of the content of the string variable, \"locationAddress\". Please

Answer 1

Here is a very simple way to do this using regex replacement in Java:

String input = "abcdefghij";
input = input.replaceAll("(.)(.)", "$2$1");
System.out.println(input);

badcfehgji

The idea is to walk down the string, starting at the beginning, capturing two characters at a time, in two different capture groups. Then, just swap those two captured characters in the replacement.

Answer 2

Here's one solution with StringBuilder:

public static String swapAdjacentPairs(String s) {
    StringBuilder sb = new StringBuilder(s);
    // divide 2 and then multiply by 2 to handle cases where the string length is odd
    // we always want an even string length
    // also note the i += 2
    for (int i = 0 ; i < (s.length() / 2 * 2) ; i += 2) {
        swapAdjacent(sb, i);
    }
    return sb.toString();
}

private static void swapAdjacent(StringBuilder sb, int index) {
    char x = sb.charAt(index);
    sb.setCharAt(index, sb.charAt(index + 1));
    sb.setCharAt(index + 1, x);
}

Usage:

System.out.println(swapAdjacentPairs("abcdefghi"));

Answer 3

A solution using Stream:

String input = "abcdefghijk";
String swapped = IntStream.range(0, input.length())
        .map(i -> i % 2 == 0 ? i == input.length() - 1 ? i : i + 1 : i - 1)
        .mapToObj(input::charAt)
        .map(String::valueOf)
        .collect(Collectors.joining());
System.out.println(swapped); // badcfehgjik

The swapping is driven by the index i. If i is even and there is a next (i+1) character then it's used. If i is odd then the previous (i-1) character is used.