Swap letters in a string

Question

I need to swap letters in a string with the following rules:

• A is replaced by T
• T is replaced by A
• C is replaced by G
• G is replaced

Answer 1

I would go for a more general solution like this:

public String tr(String original, String trFrom, String trTo) {
  StringBuilder sb = new StringBuilder();

  for (int i = 0; i < original.length(); ++i) {
    int charIndex = trFrom.indexOf(original.charAt(i));
    if (charIndex >= 0) {
      sb.append(trTo.charAt(charIndex));
    } else {
      sb.append(original.charAt(i));
    }
  }

  return sb.toString(); 
}

Calling the function like this would give the result you need:

tr("ACGTA", "ATCG", "TAGC")

So the function is pretty much the same as unix tr utility:

echo ACGTA | tr ATCG TAGC